Its too bad that both can't attend the same school. Your son will most likely adapt to his new school and class and be just fine once he has made a few friends. It may be to his advantage that his sister isn't in the same school as a forced independence if he has been dependent on her. I think the hardest part is on the parents because so often it is the parents that have to drive to two schools, attend teachers meetings at two schools and attend activities at two schools. My thought is that is will be much harder on the parents than the children.