J.S.
I have potty trained children in a school setting and I have also assisted other parents in home with potty training their children as part of early intervention therapy. You said that everything was fine until he started school... Have you talked to the teachers at school to find out their potty routine? Consistancy is key with potty training. Does the school take the children for group potty breaks? Do the children have to ask to use the potty? Are they assisting the children in the bathroom and to what extent? Did he have an accident at school and get embarassed? I would ask the school some of these questions first to troubleshoot a bit. Parents tend to know when their child needs to use the potty, teachers have a lot more children to look after and may miss the subtle cues a child is giving and if the child is shy he may not speak up to ask. A potty training schedule might work well to avoid accidents until he is back to his old routine again. Set an egg timer and bring him to the potty every 60-90 minutes. And really reinforce the successes, a special toy or treat that is only for when he uses the potty and no other time. Hope this helped.