People with Asperger syndrome aren't stupid, only without the necessary astuteness or intution to notice some things. Do you remember when you are playing cards with your friends and anybody has got his pocker-face? An Aspie can't discover those little details, for example when somebody is lying.
Anytimes they can't find the right words. For example.
- Why not to eat more fruit, it is good for health!
- Do you mean I am too fat?
- Oh no! (Ups!).
Or in a debate an aspie isn't enough fast to improvise an ingenious response but maybe the next time it has a ready answer you could be surprise with a really good words from his memory.
And sometimes the mind is too frozen, without enough mental flexibility to adapt to new changes.
And in the past when this was not enough known, people with Asperger were tagged as... no-bright.
* My advice is the construct races (for example androids, warforgeds or sharminds) are the softest way to play a character with autism.