Originally Posted by Portia
Here is the big difference... With autism, the obsessiveness is very repetitive. For example, when seeing the number 5, he will say 5, but that really is all there is to it. When it is gifted obsessive, he studies the number, the traits or properties, he manipulates the number, he experiments what happens if adding or subtracting one, he expresses it creatively, and he innovates with the information he has.

I disagree with this description. The gifted/autistic (one can be both) can be highly creative in the manipulation of information, while still showing restricted interests.

That the OP's DS won't engage with the preschool's activities may be a red flag for autism. I'd start right away trying to increase flexibility by using the area of interest as a springboard into other activities.