Thanks acs. I'm not so sure if DS cares about what the other kids are doing, and he hasn't complained about them. I think it's more of he just doesn't want to do it if he's already done it before. Also, I haven't had a chance to talk enough to the teacher to know if the projects he doesn't want to do are more craft-related or academic-related, but I assumed from her comment it was more something she was trying to teach. If it's arts and crafts - he's just never really liked to do them, and maybe he's just sick of it.
I do like the idea of giving him a challenge. He does have a sort of challenging thing right now - we're making him take swimming lessons and he's pretty apprehensive about the whole thing and has tried to avoid it for 2 years now. Not sure if that counts, but I could talk to him about struggles and other kids. Although I'm not sure that the issues are related right now, it's still a good idea.
I'm not sure if he's getting anything he likes at preschool.

He has complained that they don't have regular legos and he doesn't like any of the toys (although the teacher said he liked pattern blocks - maybe he's sick of those if that's the only thing). And he really has never been a kid who likes crafts. I'm not sure if there would be another preschool that would fit (we don't have a lot of choices). Of course, I could be premature in my worries - there could be something else that we'll learn in conferences, or maybe we could donate some materials to the classroom.