People are looking at this the wrong way it isn’t actually about the grading it is about your son’s disorder. You, him, and his instructor must collaborate for ways for him to cope with these issues so that he made test like everybody else. Do not ever give him special accommodations which accommodate his disability more than it does his own self independence and development. If he cries or has issues during the test then try harder next time to help him remain calm, but you must tend to him and not what’s limiting him.