In addition to what Cricket2 has suggested, I would contact the teacher and politely say that you're following up with previous conversations and are wondering what is being done in the classroom to challenge him now? Be careful to not take too confrontational of a tone...just be "asking." Then, you'll have the info as to what's going on NOW and you can suggest specific options (like what Cricket2 said) to increase that further. You will need to be specific -- if the school thinks that what they're doing right now IS "challenging" him (and if he's being compliant and acting fine at school, they may think everything is just perfect) then they believe they're meeting his needs and responding to your request.
