I noted that IQ's in these children are for the most part normal. In my son's case, he refused to do the work. He's been in special ed for most of his school years.
Is it possible that your son was being distracted by the other kids?
My daughter has an arangement wher she is in classes for lab-work, lecture or group activities, but for written work or tests or quizzes, she goes to her couselor's office where she can work quietly without aggitation. Her grades shot up when this was figured out
Many kids with autism simply get overwhelmed by distractions.
It's difficult to test for IQ in children who cannot talk, read, or communicate normally -- yet those of us who know autistics find that there is definitely intelligence there -- we just can't reach it. Is it normal? I have no idea. Is it creative? Often.
My son in law recently installed a whole media room in their basement with all the technology to view movies, etc. He and my daughter try to keep the instructions for DVDs etc. away from the autistic child because he will drive everyone crazy by constantly restarting the movie, or game. It's called stimming. In fact, my daughter doesn't even know how to operate the equipment.
My other daughter was visiting last week so my son in law set up a movie for everyone to watch. In just a couple of minutes of watching the movie, Andy noticed for the first time that there is a DVD player down there (a feature that they had kept hidden from him previously). Of course he focused on it and soon could operate it. None of the other children, or their mother, can operate it. Andy has his own DVD player to mess with upstairs. They really didn't want him to know about the new one! The upstairs DVD was purchased a couple of years ago because he had made such a mess out of the VHS player and tapes. Movies are his passion -- that is parts of movies. He rewinds incessently.