I have read in a book on AS that some children with this condition manage to do all right in school and the teachers hardly notice any difference in their social behaviour. When they return home though, they are mentally exhausted from the effort it took to interact with all the other children and the teachers. So once they feel they can relax among their family they let down their guards and the condition becomes more obvious. It might in fact be that your son does not look very special to his teachers.
If this is really the case with your son it might be helpful for him if he gets some time to himself when he comes home from school. Let him spend some time with his special interest or other things he enjoys doing before he has to do his homework or before he has to face more interactions with non-family-members. This will help him relax and get some mental energy back. Afterwards he will be better able to cope with the rest of the day and things will get more relaxed for all of you.
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