I would try to figure out what he means by "stupid" or "not good at anything." Questions that are open ended like "what do you feel you aren't good enough at doing yet?" or "what's happening that makes you think you are stupid?"
It's possible that he's experiencing more challenge and isn't used to it in an academic environment. We are seeing this with our DS (8) and cursive writing. He's down on himself and worried he won't ever do it right (he's been learning it for two weeks, but it isn't coming as fast as the rest of his academic pursuits).
