I agree with Val. All three of mine started in a French immersion school, and in the younger years, most of the instruction is in French. Most of the math was in French. They did not have any problems transitioning to the math in an English only school.
Their English language skills were fine too. While mine left the school in elementary, they had friends that went through middle school (the school ends with 8th grade). Those friends went to "English-only" high schools, and almost every one ended up at an Ivy or other elite school. of course, they were very bright kids, but the bilingual aspect did not seem to affect college admissions.
