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Childhood and adolescent overweight and obesity have been a global health concern in recent years with many negative implications for children's health and development. Previous research has suggested that as compared to normal weight children, children who are overweight or obese perform worse academically (Falkner et al., 2001), have more emotional problems (Storch et al., 2007; Zavodny, 2013), and encounter more problems in their interpersonal relationships with peers (Gable et al., 2012). These findings, however, are not always consistent. Three major limitations in the literature can be identified. First, many studies of the associations between children's and adolescents' weight or BMI and developmental outcomes have relied on BMI from a single-time point without considering the trajectory of children's and adolescents' weight development. To study the cumulative effects of overweight and obesity, it is important to examine children's and adolescents' weight patterns and to address questions such as whether children and adolescents who are consistently overweight are at higher risk for negative outcomes than are children and adolescents who become overweight over time. Second, most studies did not have nationally representative samples that would allow for an examination of ethnic differences. Third, no study has examined the protective (moderating) role of parenting when investigating the influence of children's and adolescents' weight trajectories on developmental outcomes. To overcome the above limitations of previous research, I used data from a nationally representative subsample of children in the Early Childhood Longitudinal Study, Kindergarten 1998-99 cohort (ECLS-K). First, I identified adolescents' different BMI trajectories across kindergarten to eighth grade by using Nagin & Land's (1993, 2012) group-based trajectory modeling (GBTM). Second, because previous research had shown ethnic and gender differences in the rates of childhood overweight as well as varying patterns of weight development, the influence of gender and ethnicity on weight trajectory membership was examined. Third, I examined the associations between different BMI trajectories and academic achievement, emotional outcomes, and peer relationships in eighth grade. Fourth, I explored the effects of parental warmth and parental involvement on these associations. I focused on parental warmth and involvement because previous research (e.g., Rohner's Parental Acceptance-Rejection Theory and Epstein's Framework of Six Types of Parental Involvement) had shown these as positive aspects of parenting practices that were associated with favorable academic achievement, emotional outcomes, and peer relationships. These parenting practices may serve as protective factors against negative developmental outcomes for adolescents in the higher risk BMI trajectory groups. Fifth, I examined whether the protective effects of parental factors varied by gender. Due to limited sample sizes for ethnic minority groups’ various BMI trajectory groups, this question was not examined for ethnicity. I identified three distinct BMI trajectories for the total sample as well as for boys and girls separately: consistently low to normal BMI group (~64-66%), gradually increasing BMI group (~27-29%), and consistently higher BMI group (~6-7%). Although there were no gender differences in trajectory group membership, there were ethnic differences in trajectory group membership. White and Asian adolescents were more likely than were Black and Hispanic adolescents to be in the consistently low to normal BMI trajectory group, whereas the latter two groups were more likely than the former two groups to be in the gradually increasing BMI trajectory group and consistently higher BMI trajectory group. Adolescents in the gradually increasing BMI group and consistently higher BMI group were shown to have less favorable academic achievement, emotional outcomes, and peer relationships compared to adolescents in the consistently low to normal BMI group. In terms of the protective role of parental warmth, the most consistent results were that parental warmth in eighth grade played a protective role for girls, but not for boys, suggesting important gender differences in the influence of parental warmth on adolescents' school achievement in the context of overweight and obesity. Parental involvement showed complex and mixed results. These results suggest that the protective and non-protective effects of parenting factors depend on the gender of the child, type of parenting factors, and specific outcome in the context of adolescent overweight and obesity.