Rachsr: May I also suggest that you volunteer in your child's classroom, if you have the opportunity? It's quite an illuminating experience. There are a number of reasons why your son may not be doing his work in class. It's helpful to see it from a classroom perspective.
That is a very good suggestion. When dd13 was in third grade, they had a number of teacher changes near the end of the year and dd stopped doing her math work and was missing things I knew she knew. I went in and observed from the back of the classroom one day. Dd was reading a book on her lap throughout the entire math period and, when called on, didn't seem to know the answers b/c she had no idea what the teacher had just been talking about.
