A lot of kids' French from English school are probably as broken as our English :). If you really want your kid to be good at in French, maybe he/she can just go through elementary education in French program and then go to normal English middle school. It's a little bit demanding for the kid but it may worth a try. However, when the kid go to the French School, you have to make sure after school he can mingle easily with English spoken kids and thus when he/she ba back to English school, at least they can talk English without accent.