The aims of the thesis were to study (1) day care and school education of Finnish migrant children in Sweden, with respect to verbal, cognitive and identity development, (2) language as a tool of thought and the role of bilingualism in children's cognitive development, primarily with respect to Finnish children in Sweden, and (3) ethnic and individual identity of Finnish children and adolescents in Sweden and Finland. These issues are studied by means of literature reviews (Summary report and Study 1 ) and empirical studies (Study 2 and Study 3). Study 1 surveys theories and research with relevance to three organizational models of school education for immigrant children in the comprehensive school: (1) regular Swedish classes, (2) home language classes and (3) composite classes, with varying proportions of instruction in the migrant children's mother tongue and in Swedish. In Study 2, language as a tool of thought was studied in 13 Finnish children at the ages of 4-7 years, attending two Finnish language day nurseries in Stockholm. Theoretically, the study was based on Lev Vygotsky's theory of thought and language, and on the hypothesis of Jim Cummins of two types of language competence, Cognitive/Academic Language Proficiency (CALP), and Basic Interpersonal Communicative Skills (BICS). Several methods were used: observations, interviews, various tests on cognitive development, and questionnaires filled by parents and day nursery staff. In Study 3, cognitive and emotional contents of Finnish identity were analyzed in three groups of Finnish comprehensive school pupils, grades 4-9: (1) 103 re-migrated pupils (former Finnish migrant children in Sweden, who have migrated back to Finland with their Finnish parents), (2) 103 Finnish pupils, who have lived their whole life in Finland, and (3) 75 Finnish pupils living in Sweden, attending Finnish home language classes. The pupils wrote an essay on ”What it is like to be a Finn”. Quantitative content analysis was used to study the contents of the essays. It is concluded that Finnish home language classes and home language day nurseries are good alternatives to the Swedish ones, with regard to the children's verbal, cognitive and identity development. The results of Study 2 stress the importance of using several different methods in studying language as a tool of thought in children, and contribute to the doubts that have been expressed about the hypothesis of BICS and CALP, for not sufficiently noticing non-verbal factors. Study 3 shows that the cognitive and emotional contents of Finnish identity develop differently in Sweden and in Finland. For example, the Finnish identity of the pupils who had grown up in Finland was both a national identity (concerned with Finland as a nation and a country) and a cultural identity (concerned with the Finnish language and Finnish way of life), whereas the Finnish identity among Finnish pupils in Sweden seemed to be almost exclusively a cultural identity. Re-migrant pupils took an intermediate position between the two groups. These differences are discussed in the Summary report, as well as contradictory results from previous studies of ethnic identity and self-concept of Finnish children and adolescents.