In the classroom, the quality of teaching is the #1 thing that influences good outcomes in kids. Not a second language. As a parent, the tiny pool of qualified French teachers is what kept me from considering French Immersion. Someone else mentioned ESL kids, and yes we have quite a few English language learners in my school, but most of them are fluent in English by grade 1... and those that are not are removed from the classroom for English instruction so it does not affect anyone else.