Our co-op has 2 early childhood teachers that are paid to be there full time and do all the curriculum. There are only 20 kids in the program (in 2 classrooms - they shuffle the kids 3X during the year. The shuffle is very intentional in terms of kid's temperaments and needs). You get to know the families and the kids really well. Co-ops are very family/teacher dependent in terms of quality. I would guess the majority of kids in this school are MG+ based on the population it is serving. It is a really great set up for us. I can't think of a better fit for my DD. Our volunteer requirements are actually quite minimal at our co-op. The day to day routine is actually more structured and stable than my son's high buck preschool.
So at the end of the day, I personally think all schooling comes down to the teacher who is going to be with your child most of the time. Is it a teacher who pigeon holes the kids or does the teacher honor each child as an individual with strengths and weaknesses?