Student teachers

I've been enjoying getting to know our current student teacher and at the same time I've been thinking a LOT about how we train our teachers.
I've watched teachers at our school who are unable to give over control to a student, some struggle over knowing what role they play (and probably end up doing more than they should), and others step completely to the side.
I know it's an important and necessary part of the process--for student teachers to be put behind the steering wheel of a classroom, but I'm less sure whether we've found the best way to implement this stage to get the needed and best training for the student.
I'm curious about the idea of a laboratory school. Would it create a more stable learning environment with opportunities to do projects that wouldn't be possible in someone else's classroom? It could be a satellite school that takes student teachers from all the colleges and universities throughout a state, with a teacher/mentor for each grade--who's always there and ready to lend a hand or ear.