DS6 (K) has been given the opportunity to do independent work on the computer during class math time. Any recommendations? I don't do stuff like this with my kids at home, so I'm kind of clueless. I am assuming it needs to be free, though perhaps I could pay for a subscription and have him use the password at school--not sure.

I don't really know his level. I guess he's kind of all over the place, but probably not above 2nd grade. It would be good for whatever he uses to assess him.