The circulation of knowledge and educational innovations at the beginning of the twentieth century followed the growth of public educational systems. It led to complex exchanges and configurations due to the crossing of different national traditions, ideas and practices. The organisation of homogeneous classrooms according to the mental development of students and of special classes for children with learning difficulties and personality troubles are examples of this process. In the elementary schools of Belo Horizonte, Brazil, special classes for the "mentally retarded" were part of a reform of the public educational system promoted by the local government in 1927. The reform was implemented during the 1930s under the supervision of the Belo Horizonte Teachers Training College, where foreign specialists were hired to head the Laboratory of Psychology and to help in the organisation of homogeneous classrooms. The Laboratory of Psychology was established in 1928 by the French psychiatrist Théodore Simon (1873–1961), who had been invited for the task, and its directorship was assumed subsequently by two Russian psychologists who had worked as assistants to Claparède at the Rousseau Institute in Geneva (Léon Walther [1889–1963], in the first semester of 1929, and Helena Antipoff [1892–1974] from 1929 till 1944). The purpose of this paper is to study the project of special classes that were established at the time, using as sources articles published by Antipoff and her students in the periodical Infância Excepcional (Exceptional Children), edited in Belo Horizonte during the 1930s and 1940s, the correspondence Antipoff maintained with her master Édouard Claparède (1873–1940), the Swiss psychiatrist and psychologist, and a founder of the Rousseau Institute of the Sciences of Education in Geneva, and other documents concerning the works of the Belo Horizonte Teachers Training College. This article looks at how these special classes, based on the guidelines proposed by Helena Antipoff, were established, adapted and transformed within the Brazilian context. Born in Russia, Helena Antipoff studied in France (1910–1911), where she was an intern at the Binet-Simon laboratory of psychology, and Geneva (1912–1914), where she completed her studies in the sciences of education at the Jean-Jacques Rousseau Institute, where she subsequently worked as teaching assistant and researcher (1926–1929). The authors' hypothesis is that the special classes established in Belo Horizonte were designed on the basis of the European, especially the Genevan model; that they represented an example of the international flow and dissemination of knowledge, and of the building of a benchmark in the field of special education in Brazil; that they subsequently contributed to the social construction of professions related to the field of special education and of the circulation and modelling of what came to be labelled as "learning and personality troubles" in children. Special classes for the education of "retarded" children and of children with learning difficulties were established in Geneva in the beginning of the twentieth century, where Claparède had supervised the examination and selection of students and the training of schoolteachers for special education since 1901. With the foundation of the Rousseau Institute in 1912, the training of teachers and the development of methods for the examination and education of special children were assumed by the Institute's team, including Claparède, the medical doctor François Naville and Alice Descoeudres, who was responsible for the development of several methods for special education. In Belo Horizonte, the establishment of special classes for the education of "retarded" children was part of a school reform launched in 1927, inspired by New Education ideals. Under Antipoff's leadership, the Laboratory of Psychology promoted the organisation of homogeneous classrooms and of special education classes in local elementary schools, starting in 1930. Intelligence tests were adapted for the measurement of the mental development of students. In the interpretation of the results, Antipoff emphasised the role of the social environment in shaping students' cognitive abilities, and developed the concept of "civilised intelligence" to explain differences in students' performances with regard to the social level of their families. "Civilised intelligence" referred to intellectual abilities already polished by society and culture, present in mental test results. She discussed with Claparède the possibility of including a "social factor" in the interpretation of test results. In the organisation and supervision of educational activities in the special classes of Belo Horizonte, the laboratory of Psychology team adapted mental orthopaedic exercises developed in Paris by Alfred Binet and in Geneva by Alice Descoeudres. Books written by Claparède and Descoeudres were translated into Portuguese, and educational practices recommended for special classes based on their suggestions were spread among teachers who came from other Brazilian states and even from other Latin American countries to attend the Belo Horizonte Teachers College. In 1932, under Antipoff's leadership, a group of teachers, doctors and intellectuals established the Belo Horizonte Pestalozzi Society for the purpose of better developing the examination and the education of mentally "retarded" and troubled children, and of giving support for the work done in special classes in Belo Horizonte schools. The approach to special education developed at the Laboratory of Psychology and at the Pestalozzi Society became known in Brazil for its "Active school" perspective, inspired by the Genevan experience. Reports written by Antipoff's students such as Naytres Rezende show that most students who attended special classes presented normal levels of intelligence, but were psychologically disturbed. The majority of those students came from low-income families. Mental orthopaedic exercises were then adapted for the development of the "civilised intelligence" required by schools. Concerning the development of special education in Belo Horizonte, one can see that the division of classes by intellectual level, the use of intelligence tests for diagnosis, the reference to the idea of a "student tailored school" proposed by Claparède, and the dialogue with methods suggested by Alice Descoeudres provide evidence of its close relationship with the Genevan model. The ideal of a scientific pedagogy, as proposed by Claparède, was remarkable in the Belo Horizonte experience, under the leadership of the Teachers College Laboratory of Psychology. At the same time, the interpretation of mental test results as manifestations of a type of "civilised intelligence" and the adaptations of mental orthopaedic exercises in order to develop this kind of intelligence required by schools show the transformations of the model within the Brazilian context. Although the model proposed for Belo Horizonte special classes can be interpreted as deriving from the Genevan approach, more research is needed to better describe how these ideas were put into practice within the highly complex institutional context of existing schools. It is important to observe what the consequences were of the organisation of special classes for children with learning or personality troubles for the future development of the local school system and for the targeted population, i.e. children with difficulties of adaptation to a highly centralised and hierarchical school system. [ABSTRACT FROM AUTHOR]