That is an excellent question.
I am getting ready to go and testify at a trial in British Columbia where I will be asked the question you just asked me, whether we should accept students who do not master French or speak it at all at our French-language schools. A parallel can also be drawn with immersion schools.
Do the linguistic strengths or weaknesses of certain students influence other students who are trying to learn French and to master the language and culture?
Based on our experience, the answer is no. I will explain why. I am mainly talking about language learning for the youngest students, who come to us in junior kindergarten or kindergarten. That is usually when the parents choose a school for their children. We rarely see parents choose a school when their children are in grades 7 or 8. They choose the school based on language and do so when their children are very young. At that age, children are sponges who soak up information. I am not saying that those children will become perfectly bilingual, but I am saying that a young child who enters a French-language school in September can speak French in December.
There are definitely support programs and we try to group students together based on their language levels. However, there is no evidence that accepting students who do not master the language will have a negative impact on the other students.