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Handedness has been studied for association with language-related disorders because of its link with language hemispheric dominance. No clear pattern has emerged, possibly because of small samples, publication bias, and heterogeneous criteria across studies. Non-right-handedness (NRH) frequency was assessed in N = 2503 cases with reading and/or language impairment and N = 4316 sex-matched controls identified from 10 distinct cohorts (age range 6-19 years old; European ethnicity) using a priori set criteria. A meta-analysis (N[subscript cases] = 1994) showed elevated NRH % in individuals with language/reading impairment compared with controls (OR = 1.21, CI = 1.06-1.39, p = 0.01). The association between reading/language impairments and NRH could result from shared pathways underlying brain lateralization, handedness, and cognitive functions.

Objective: To report how improvements on a Brazilian language intervention for early childhood education settings (PROLIN) were made and evaluated. Study Design: In the first phase, the programme layout and materials were improved. This involved redesigning the guidelines for the programme, adding videos (using a learning management system) and creating an observation checklist to monitor the fidelity of implementation. The second phase was a two-week pilot study (a seven-session intervention) involving two teachers and 22 students. Checklists and video footage were analysed to investigate implementation. Results: Quality of implementation was generally good, but we identified additional areas for improvement. Teachers had some difficulties with aspects related to session dynamics, implementation of activities and use of techniques that reinforce learning. Conclusions: The pilot study was instrumental in identifying obstacles for a scaled-up, high-quality implementation. The design of these materials took into consideration ways of guiding and supporting teachers to: (1) offer students adequate participation time; (2) help include children who are shy or have behaviour problems; (3) use teaching strategies properly; (4) bring sessions to a close; and (5) reach the objectives of each session. Further modification is still needed, especially in the manual, videos and supplementary materials.

Background: There is now substantial evidence that language interventions delivered to small groups can be effective for improving language skills and hence strengthening the foundation for formal schooling. However, there are remaining challenges when delivering such interventions in naturalistic environments at scale. Method: We reflect on three randomised trials designed to evaluate the impact of an early years language programme, prior to the implementation of a large effectiveness trial, delivered in partnership with speech and language professionals. We consider findings within a framework from implementation science. Results: We found that, in contrast to policy-led interventions for reading and mathematics, language interventions are not prioritised in mainstream settings. Aside from this, other obstacles to delivery were the time taken to prepare and to timetable sessions, lack of communication about the requirements of delivery and the need for language screening. Crucial to success was the support from the class teacher of teaching assistants delivering the intervention. However, feedback was largely positive from most stakeholders, and the intervention was found to have a positive impact on children's language with preliminary evidence for effects on behaviour and on reading comprehension. Conclusions: While many educators recognise the importance of language for communication, the benefits of oral language interventions are only recently becoming prioritised by policy-makers. We propose that challenges to successful delivery and adoption of evidence-based language interventions in mainstream settings can be remedied through better communication with stakeholders and collaboration between researchers and professional colleagues including senior leaders, teachers, teaching assistants, speech and language therapists and psychologists. It is imperative to take account of issues of implementation when designing an intervention and to do this successfully is a multidisciplinary enterprise.

Children with language learning difficulties frequently display problems learning grammar. One such group is children with Down syndrome. This study evaluates the effectiveness of an intervention to teach the use of the regular simple past tense to children with Down syndrome. Trained teaching assistants delivered the intervention for 20 min per day for 10 weeks. We conducted a Randomised Controlled Trial, with a waiting list control design in which the Intervention group (N = 26) received the intervention immediately, while the delayed intervention group (N = 26) received the intervention later. Immediately following the intervention, the intervention group showed significantly larger gains in the use of regular simple past tense forms (d = 1.63 on a composite measure of simple past tense formation) as well as generalisation to verbs not explicitly taught. In addition, following the intervention children made overregularisation errors by incorrectly using regular simple past tense marking for irregular verbs; such errors support the claim that children had acquired generative knowledge underlying past tense marking. The delayed intervention control group showed identical benefits from the intervention when they received it, and the gains shown by the intervention group were maintained at follow up testing. This study shows that children with Down syndrome, who display severe language difficulties, can be taught to use simple past tense marking. The theoretical and applied implications of these findings for understanding the nature, causes and treatments of children's language difficulties are discussed.

Morphemes, the smallest meaning-bearing units of language, recur in many words. Therefore, morphological knowledge can facilitate the comprehension of novel words. This study tested the effectiveness of a morphological training program on children's learning and retention of exposed words and morphologically related unexposed words compared with an active control condition. Norwegian second graders (N = 717) unselected for ability were individually randomized to either a morphological (n = 366) or a mathematical training program (n = 351). Both programs lasted for 8 weeks and were delivered as self-contained apps in a classroom setting. The morphological training built on the principle that frequency of target elements together with variation of nontarget elements can support implicit learning. Treatment-blind examiners assessed participants' meaning-based knowledge (word comprehension and definitions) and code-based knowledge (word reading fluency and spelling) at pretraining, immediately post training, and at follow-up 6 months later. An intention-to-treat analysis showed lasting effects of the morphological training on meaning-based knowledge of exposed words (posttest: d = 0.37; follow-up: d = 0.31) and unexposed words containing trained morphemes (posttest: d = 0.27; follow-up: d = 0.27) and code-based knowledge of exposed words (posttest: d = 0.22; follow-up: d = 0.13). For code-based knowledge of unexposed words, there were significant training effects at the posttest (d = 0.12) but not follow-up (d = 0.05). There were no significant effects on a far-transfer measure of general vocabulary. These results demonstrate that a brief morphological training program can produce lasting and educationally meaningful gains in students' word knowledge.

Visual information conveyed by a speaking face aids speech perception. In addition, children's ability to comprehend visual-only speech (speechreading ability) is related to phonological awareness and reading skills in both deaf and hearing children. We tested whether training speechreading would improve speechreading, phoneme blending, and reading ability in hearing children. Ninety-two hearing 4- to 5-year-old children were randomised into two groups: business-as-usual controls, and an intervention group, who completed three weeks of computerised speechreading training. The intervention group showed greater improvements in speechreading than the control group at post-test both immediately after training and 3 months later. This was the case for both trained and untrained words. There were no group effects on the phonological awareness or single-word reading tasks, although those with the lowest phoneme blending scores did show greater improvements in blending as a result of training. The improvement in speechreading in hearing children following brief training is encouraging. The results are also important in suggesting a hypothesis for future investigation: that a focus on visual speech information may contribute to phonological skills, not only in deaf children but also in hearing children who are at risk of reading difficulties. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=bBdpliGkbkY.

Impaired procedural learning has been suggested as a possible cause of developmental dyslexia (DD) and developmental language disorder (DLD). We evaluate this theory by performing a series of meta-analyses on evidence from the six procedural learning tasks that have most commonly been used to test this theory: the serial reaction time, Hebb learning, artificial grammar and statistical learning, weather prediction, and contextual cuing tasks. Studies using serial reaction time and Hebb learning tasks yielded small group deficits in comparisons between language impaired and typically developing controls (g = -0.30 and -0.32, respectively). However, a meta-analysis of correlational studies showed that the serial reaction time task was not a reliable correlate of language-related ability in unselected samples (r = 0.03). Larger group deficits were, however, found in studies using artificial grammar and statistical learning tasks (g = -0.48) and the weather prediction task (g = -0.63). Possible reasons for the discrepancy in results from different tasks that all purportedly measure procedural learning are highlighted. We conclude that current data do not provide an adequate test of the theory that a generalized procedural learning deficit is a causal risk factor for developmental dyslexia or developmental language disorder.

Background: There is increasing recognition of the contribution of morphological skills to the development of reading fluency. However, theoretical models and recent research raise questions about how different language skills influence reading development. Methods: The present study was designed to follow the reading development of a large sample of Norwegian children (N = 323) from preschool to Grade 9, assessing their performance on a wide range of language-related and reading skills including morphological awareness. We employed confirmatory factor analyses of the cognitive, linguistic and reading variables prior to modelling the contribution of the preschool language variables to reading comprehension in Grades 1, 2 and 9. Results: Preschool measures of phonological, morphological and semantic skills were best represented by a single language latent variable. Reading in Grades 1 and 2, assessed by measures of both decoding and comprehension, was also best represented by a single latent variable. Preschool language skills have long-range direct and indirect effects on the development of reading comprehension. Overall, preschool language abilities accounted for 69.2% of the variance in reading comprehension 9 years later. Conclusions: The results demonstrate the powerful influence of early language on later reading and suggest that language intervention programmes, combining phonological, morphological and semantic activities, may help to reduce the incidence of reading problems.

This study examined the longitudinal relationship between early handwriting skills and the growth of spelling and reading skills in a large sample (N = 569) of 5- to 6-year-old children unselected for ability. The quality of children's handwriting was assessed using five indicators (letter form, slant, rhythm, ability, general appearance). Children also completed a wide range of tasks measuring reading, spelling and literacy-related skills (letter-sound knowledge, phoneme awareness, rapid automatized naming). A latent variable path model showed that variations in handwriting skills, but not generic fine motor skills, accounted for unique variance in the growth of spelling, but not reading. Theoretically, these findings suggest that writing words may lead to the creation of motoric representations of spelling patterns that support the development of children's orthographic knowledge. From an applied perspective, our findings suggest that practice writing words may help children to learn to spell them.

The procedural deficit hypothesis claims that impaired procedural learning is a causal risk factor for developmental dyslexia and developmental language disorder. We investigated the relationships between measures of basic cognitive processes (declarative learning, procedural learning and attention) and measures of attainment (reading, grammar and arithmetic) in a large sample of 7- and 8-year-old children. A latent variable path model showed that verbal declarative memory skills predicted attainment but were not significantly related to attention. Procedural learning was only weakly related to measures of attainment and attention assessed during the procedural learning task accounted entirely for its relationship with measures of attainment. Our results challenge the procedural deficit hypothesis of reading and language disorders, but suggest that attentional skills (rather than procedural learning ability per se) may be an important predictor of reading, arithmetic and grammatical skills.

Purpose: Speechreading (lipreading) is a correlate of reading ability in both deaf and hearing children. We investigated whether the relationship between speechreading and single-word reading is mediated by phonological awareness in deaf and hearing children. Method: In two separate studies, 66 deaf children and 138 hearing children, aged 5-8 years old, were assessed on measures of speechreading, phonological awareness, and single-word reading. We assessed the concurrent relationships between latent variables measuring speechreading, phonological awareness, and single-word reading. Results: In both deaf and hearing children, there was a strong relationship between speechreading and single-word reading, which was fully mediated by phonological awareness. Conclusions: These results are consistent with ideas from previous studies that visual speech information contributes to the development of phonological representations in both deaf and hearing children, which, in turn, support learning to read. Future longitudinal and training studies are required to establish whether these relationships reflect causal effects.

We assessed a range of theoretically critical predictors (numerosity discrimination, number knowledge, counting, language, executive function and finger gnosis) of early arithmetic development in a large unselected sample of 569 children at school entry. Assessments were repeated 12 months later. Although all predictors (except finger gnosis) were moderate to strong correlates of arithmetic, a latent variable path model showed that only number knowledge and numerosity discrimination were unique predictors of arithmetic development over the 1st year of formal education. These findings are consistent with the Triple Code Model (Dehaene & Cohen, 1995) suggesting that both nonsymbolic representations of numerosity and visual symbolic representations of number are critical for the development of arithmetic. Our results suggest that the assessment of numerosity judgments and Arabic number knowledge at school entry may be useful for identifying children at risk of difficulties in acquiring arithmetic skills.

It is now widely accepted that phonological language skills are a critical foundation for learning to read (decode). This longitudinal study investigated the predictive relationship between a range of key phonological language skills and early reading development in a sample of 191 children in their first year at school. The study also explored the theory that a failure to establish automatic associations between letters and speech sounds is a proximal causal risk factor for difficulties in learning to read. Our findings show that automatic letter-sound associations are established early, but do not predict variations in reading development. In contrast, phoneme awareness, letter-sound knowledge and alphanumeric RAN were all strong independent predictors of reading development. In addition, both phoneme awareness and RAN displayed a reciprocal relationship with reading, such that the growth of reading predicted improvements in these skills.

International assessments show that 20% of adolescents cannot read simple texts with understanding. Despite this, research has focused on early reading in childhood and skilled reading in adulthood, neglecting reading development during adolescence. We report a longitudinal study assessing reading and vocabulary development at 12, 13 and 14 years in a sample of 210 adolescents who were unselected for ability. Word reading accuracy, word reading fluency, reading comprehension, receptive vocabulary and expressive vocabulary were assessed using standardized assessments. Latent variable models showed consistent rank order amongst individuals (high stability), significant progress over time, and evidence that achievement gaps between the least and most able adolescents were narrowing. Oral vocabulary knowledge and reading comprehension were best conceptualized as indices of a common language construct. Low levels of reading proficiency were also observed in a substantial proportion of this sample, underlining the importance of providing ongoing reading and language support during adolescence.

Dyslexia is a difficulty in learning to decode (read aloud) and to spell. DSM5 classifies dyslexia as one form of neurodevelopmental disorder. Neurodevelopmental disorders are heritable, life-long conditions with early onset. For many years, research on dyslexia proceeded on the basis that it was a specific learning difficulty -- specific meaning that the difficulty could not be explained in terms of obvious causes such as sensory problems or general learning difficulties (low IQ). However, the failure to find qualitative differences in reading, and phonological skills, between children with dyslexia and children with more general learning problems led this kind of 'discrepancy' definition to fall from favour. The Rose Review stated that dyslexia can occur across the IQ range and that poor decoding skills require the same kinds of intervention irrespective of IQ. In this paper, we argue that loosening the criteria for dyslexia has influenced common understanding of the condition and led to diagnostic confusion. In the longer term, the use of the term may need to change. Implications for research and practice are discussed.

Purpose: We developed and evaluated in a randomized controlled trial a computerized speechreading training program to determine (a) whether it is possible to train speechreading in deaf children and (b) whether speechreading training results in improvements in phonological and reading skills. Previous studies indicate a relationship between speechreading and reading skill and further suggest this relationship may be mediated by improved phonological representations. This is important since many deaf children find learning to read to be very challenging. Method: Sixty-six deaf 5- to 7-year-olds were randomized into speechreading and maths training arms. Each training program was composed of a 10-min sessions a day, 4 days a week for 12 weeks. Children were assessed on a battery of language and literacy measures before training, immediately after training, and 3 months and 11 months after training. Results: We found no significant benefits for participants who completed the speechreading training, compared to those who completed the maths training, on the speechreading primary outcome measure. However, significantly greater gains were observed in the speechreading training group on one of the secondary measures of speechreading. There was also some evidence of beneficial effects of the speechreading training on phonological representations; however, these effects were weaker. No benefits were seen to word reading. Conclusions: Speechreading skill is trainable in deaf children. However, to support early reading, training may need to be longer or embedded in a broader literacy program. Nevertheless, a training tool that can improve speechreading is likely to be of great interest to professionals working with deaf children.

The two major determinants of reading comprehension are language comprehension and decoding, but prior studies of the development of reading comprehension from an early age show inconsistent results. To clarify these inconsistencies we report a 6-year longitudinal study (starting at Age 4 years) where we control for measurement error and track the development and interrelationships between a range of predictors of reading comprehension (language, decoding, and cognitive skills). We found two main pathways to reading comprehension: a highly stable language comprehension pathway (reflecting variations in vocabulary, listening comprehension, grammar, and verbal working memory) and a less stable code-related pathway (reflecting variations in phoneme awareness, letter knowledge, and rapid automatized naming). Early language comprehension at Age 4 years is strongly related to code-related predictors (phoneme awareness, letter knowledge, and rapid naming), and influences decoding indirectly through these constructs. Early oral language skills predicted initial levels of reading comprehension and its growth between the ages of 7 and 9 years. Strikingly, language comprehension and decoding, together with their interaction and curvilinear effects, explain almost all (99.7%) of the variance in reading comprehension skills at 7 years of age. Our study adds to prior knowledge in several important ways and provides strong support for an elaborated version of the simple view of reading (Gough & Tunmer, 1986).

The present paper reports a secondary analysis of data from a published randomised controlled trial. This paper compares the outcomes of children with specific language impairment (SLI) and those with a general delay (GD) following participation in either an oral language intervention or a phonology with reading intervention. Sixty-eight children were included in the analysis, 29 with SLI and 39 with a general delay. The interventions were delivered by trained teaching assistants on a daily basis during a twenty-week period for small group and individual work. Performance on measures of language and literacy at the end of the intervention period and after a 5-month delay indicated better response to the phonology with reading intervention for the SLI group. There was no difference between the SLI and GD groups in response to oral language intervention. Findings are discussed with reference to the role of non-verbal IQ in literacy development. (Contains 3 tables, 1 figure and 1 endnote.)

Speech perception deficits are commonly reported in dyslexia but longitudinal evidence that poor speech perception compromises learning to read is scant. We assessed the hypothesis that phonological skills, specifically phoneme awareness and RAN, mediate the relationship between speech perception and reading. We assessed longitudinal predictive relationships between categorical speech perception, phoneme awareness, RAN, language, attention and reading at ages 5.5 and 6.5 years in 237 children many of whom were at high risk of reading difficulties. Speech perception at 5.5 years correlated with language, attention, phoneme awareness and RAN concurrently and was a predictor of reading at 6.5 years. There was no significant indirect effect of speech perception on reading via phoneme awareness, suggesting that its effects are separable from those of phoneme awareness. Children classified with dyslexia at 8 years had poorer speech perception than age-controls at 5.5 years and children with language disorders (with or without dyslexia) had more severe difficulties with both speech perception and attention control. Categorical speech perception tasks tap factors extraneous to perception, including decision-making skills. Further longitudinal studies are needed to unravel the complex relationships between categorical speech perception tasks and measures of reading and language and attention.

This study investigates the longitudinal predictors of the development of Chinese word reading skills and potential bidirectional relationships between Chinese word reading and oral language skills. We examine, in a 2-year longitudinal study, a wide range of theoretically important predictors (phonological awareness, tone awareness, morphological awareness, visual skills, rapid automatized naming, Pinyin knowledge, and vocabulary knowledge) of reading in 143 primary-school children living in mainland China. Initial levels of reading were predicted by vocabulary knowledge, phonological awareness, and visual discrimination skills. Only initial reading levels predicted growth in reading. Initial reading also predicted growth in vocabulary knowledge and morphological construction. This pattern demonstrates that the early stages of learning to read in Chinese places demands on semantic (vocabulary) and visual skills in addition to phonological skills. Furthermore, early levels of word reading predict the growth of vocabulary knowledge and morphological awareness suggesting that the development of these oral language skills is facilitated by learning to read.

We followed children at family risk of dyslexia and children with preschool language difficulties from age 3½, comparing them with controls (N = 234). At age 8, children were classified as having dyslexia or Developmental Language Disorder (DLD) and compared at earlier time points with controls. Children with dyslexia have specific difficulties with phonology and emergent reading skills in the preschool period, whereas children with DLD, with or without dyslexia, show a wider range of impairments including significant problems with executive and motor tasks. For children with both dyslexia and DLD, difficulties with phonology are generally more severe than those observed in children with dyslexia or DLD alone. Findings confirm that poor phonology is the major cognitive risk factor for dyslexia. [The Wellcome Language and Reading Project Team authored this article in addition to the listed authors.]

The present study investigated the moderating role of orthographic consistency on the development of reading comprehension in four language groups (English, n = 179; Spanish, n = 188; Czech, n = 135; Slovak, n = 194) from kindergarten to Grade 2. In all languages, early variations in phoneme awareness/letter knowledge, rapid automatised naming, and emerging decoding skills, but not oral language, predicted variations in decoding skills at the end of Grade 1; these in turn predicted reading comprehension in Grade 2. For the three consistent orthographies (Spanish, Slovak, and Czech), kindergarten language skills were another significant predictor of Grade 2 reading comprehension. This effect was absent in the English sample, where variations in decoding skills were a more powerful predictor. These results provide the first longitudinal evidence for effects of orthographic consistency on the development of reading comprehension and provide support for the simple view of reading.

Background: Although language and communication difficulties are common in secondary school students, there has been limited research into the efficacy of interventions for adolescents with language and communication difficulties. Aims: To investigate the efficacy of teaching assistant (TA)-delivered narrative and vocabulary interventions to mainstream secondary school-aged students with language disorder. Methods & Procedures: A randomized controlled trial (RCT) of a language and communication intervention was used to evaluate the efficacy of vocabulary and narrative interventions to improve the vocabulary and narrative performance of adolescents (mean age = 12.8 years) with language disorder. The language and communication programmes (narrative, vocabulary and combined narrative and vocabulary) were delivered by TAs in the classroom, three times per week, for 45-60 min each, over 6 weeks, totalling 18 sessions. Standardized and intervention-specific measures were used as outcomes. Outcomes & Results: Twenty-one schools with 358 eligible participants were recruited. The three intervention groups showed significant improvements (d = 0.296) on a narrative latent variable defined by a standardized narrative assessment (the Expression, Reception and Recall of Narrative Instrument--ERRNI), but there were no significant improvements on an overall vocabulary latent variable compared with the waiting control group. Differential effects were found on some non-standardized intervention-specific measures with the narrative group making significantly more progress on narrative tasks compared with the waiting control group, the vocabulary group showing the same pattern on specific vocabulary tasks, and the combined narrative and vocabulary group making significantly more progress on some of the intervention-specific narrative, and all the intervention-specific vocabulary outcomes compared with the waiting control group. Conclusions & Implications: It is possible to improve narrative but not vocabulary skills, as assessed by standardized measures, in secondary school students with a relatively brief group TA-delivered intervention. There were differential effects for both narrative and vocabulary with intervention-specific measures. Future work is required to explore whether more intensive and longer lasting interventions would be more effective and to identify which students in this age group are most likely to benefit from such interventions.

For children who are born deaf, lipreading (speechreading) is an important source of access to spoken language. We used eye tracking to investigate the strategies used by deaf (n = 33) and hearing 5-8-year-olds (n = 59) during a sentence speechreading task. The proportion of time spent looking at the mouth during speech correlated positively with speechreading accuracy. In addition, all children showed a tendency to watch the mouth during speech and watch the eyes when the model was not speaking. The extent to which the children used this communicative pattern, which we refer to as social-tuning, positively predicted their speechreading performance, with the deaf children showing a stronger relationship than the hearing children. These data suggest that better speechreading skills are seen in those children, both deaf and hearing, who are able to guide their visual attention to the appropriate part of the image and in those who have a good understanding of conversational turn-taking.

This study examined whether variations in brain development between kindergarten and Grade 3 predicted individual differences in reading ability at Grade 3. Structural MRI measurements indicated that increases in the volume of two left temporo-parietal white matter clusters are unique predictors of reading outcomes above and beyond family history, socioeconomic status, and cognitive and preliteracy measures at baseline. Using diffusion MRI, we identified the left arcuate fasciculus and superior corona radiata as key fibers within the two clusters. Bias-free regression analyses using regions of interest from prior literature revealed that volume changes in temporo-parietal white matter, together with preliteracy measures, predicted 56% of the variance in reading outcomes. Our findings demonstrate the important contribution of developmental differences in areas of left dorsal white matter, often implicated in phonological processing, as a sensitive early biomarker for later reading abilities, and by extension, reading difficulties.

Impaired procedural learning has been suggested as a possible cause of developmental dyslexia (DD) and specific language impairment (SLI). This study examined the relationship between measures of verbal and non-verbal implicit and explicit learning and measures of language, literacy and arithmetic attainment in a large sample of 7 to 8-year-old children. Measures of verbal explicit learning were correlated with measures of attainment. In contrast, no relationships between measures of implicit learning and attainment were found. Critically, the reliability of the implicit learning tasks was poor. Our results show that measures of procedural learning, as currently used, are typically unreliable and insensitive to individual differences. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=YnvV-BvNWSo

Background: Children's vocabulary knowledge is closely related to other measures of language development and to literacy skills and educational attainment. Aim: To use a regression discontinuity design (RDD) to evaluate the effectiveness of a small-group vocabulary intervention programme for children with poor vocabulary knowledge. Methods & Procedures: The vocabulary knowledge of children (N = 199) aged 6-9 years was assessed in six classes. Based on scores at the initial assessment, children with low vocabulary scores for their age were assigned to an intervention group (43 children), with the remaining 156 children assigned to a control group. Children in the intervention group received two to three small-group weekly teaching sessions over a 10-week period. All children were retested post-intervention on the same measures of vocabulary knowledge. Outcomes & Results: The intervention group showed significant improvements in their knowledge of the meanings of the taught words at post-test (an additional 3.95 words learned [95% confidence interval (CI) = 2.70-5.20] compared with the control group; d = 1.20), but the effects did not generalize to untaught words. Conclusions & Implications: A small-group vocabulary intervention programme is effective for teaching word meanings to 6-9-year-old children with poor vocabulary skills. This study provides further evidence that the RDD is an effective method for evaluating educational interventions.