Thirty-two children who experienced difficulty in primary French immersion were compared to seven other groups of children matched for age and sex on a wide variety of language, perceptual, academic achievement, memory, motor, sensory and other tests to determine if there was anything unique in the profile of this group. The comparison groups included three groups in which language is a factor: English-speaking children in French language schools, French-speaking children in French language schools and children from other ethnic and language backgrounds in English language schools. The four "non-language" groups included standard diagnostic groups: hyperactive, minimal brain dysfunction, social and emotional maladjustment and primary reading disability. A group of eight children who were doing well in French immersion was included. To monitor their progress on academic achievement and language tests over time, follow-up testing was obtained on twenty-four children who had difficulty in primary French immersion and seven children who were doing well in French immersion. The findings support the conclusion that some children of above average potential and normal abilities for school progress in their native language experience difficulty or fail in a primary immersion program in a second language as a result of a mild specific maturational lag. (Author/CLK)