I agree with Tallulah that many kids' writing looks like that in K and it is quite typical even for advanced kids. Does your son's writing fall in that ballpark? Much worse?

I happen to have a son in K whose writing is good, and it is very obvious from the teachers' responses that this is unusual. I don't even find it that great--my DD's penmanship and ability to compose were much better at this age. I think it's because he's a boy that people flip out a little.