My 8yr old is failing but only because he sits in cl and does nothing?

I just read someone's Yahoo question about their Son failing in cl because they don't want to do anything. Well my 8yr old is the same way. My Son is very intelligent and knows what the work given to him is asking with the exception of reading comprehension. If I put him in Sylvan I feel like I'd be wasting money because he knows this stuff! It's just a matter of him doing it! I honestly don't like his Teacher and he wasn't failing this bad last year with his 2nd grade teacher. Could it just be the cl?