What do Asperger's feel when they are always alone at school?

It's not unusual for kids with Asperger syndrome to be alone at school. He might well want to join in but finds it very difficult to do. It's good of his sister to try to help him integrate. Have you asked him if he's happy being alone? Or if he wants to integrate? I was always alone at school and often did want to join in but didn't know how and when I tried was unsuccessful. I also got bullied a lot. If your son does want to integrate maybe the school could find some of the more understanding kids to befriend him.