It really depends on the individual, as pointed out above, but some typical AS impairments can be problematic when trying to drive:
1) Difficulty multitasking
2) Reaction time
The key, if your son has such impairments, will be for him to be aware and do his best to compensate. That will take time and practice. He needs a more patient instructor and he needs to allow himself whatever time he needs, rather than put it on a set time schedule. The goal is for him to be comfortable and safe driving, and he should be prepared to develop the skill in his own time and his own way, and you should help him find instruction that will allow it.
Both my husband and I have found we prefer driving stick shifts. While it adds an extra task to the mix, it also keeps your attention more firmly on the act of driving. For me, that is needed - my mind can really wander. For my husband, it just makes it more fun. Of course, I first learned to drive an automatic, and never having been a great driver, I wouldn't have thought of learning to shift if I hadn't bought a neighbor's car that happened to be one. Still, over time, I've noticed it has made me a better driver. Worth considering, anyway.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).