My opinion? Take him out of school. At his age many children still want to be with mom and with adults.
I read an article somewhere (I wish I remembered where, possible Life Learning magazine) that explains that peer experience for young children is actually bad for their social development. They need adults. Trust your child.
There is a chapter that says something similar about what is socially best for young ones in the book Raising Our Children, Raising Ourselves. So, reconsider and I would suggest trusting him and responding to his needs on his terms. He knows best what he needs.