The Development of Bilingual Proficiency is a large-scale, five-year research project begun in 1981. The final report contains three volumes, each concentrating on specific issues investigated in the research: (1) the nature of language proficiency, including second language lexical proficiency and the development and growth of metaphor comprehension in first and second languages; (2) the effect of classroom treatment of language proficiency, including a study of the Colt Observation Scheme, a core French observation study, an immersion observation study, and a classroom experiment in functional grammar in French immersion; and (3) the relevance of social context and age for language learning, including studies on the language use, attitudes and proficiency of Toronto Portuguese-Canadian children, development of bilingual proficiency and the transition from home to school in Portuguese-speaking children, the relationship of arrival age, residence length, and literacy skills among Japanese immigrant students, and the relationship between starting age and oral second language proficiency in three groups of classroom learners. Each volume contains a 20-page overview of the project and brief summaries of each individual study. (MSE)