I agree with the other posters that the tendency to be reserved can be a good thing, especially when a child is out of his comfort zone. I also suspect that many HG+ kids who are socially in-tune with their peers tend to be reserved in the classroom. I still remember the kid in 5th grade who answered every difficult math problem and the other kids would whisper **precisely** as soon as he spoke up. That said, there are lots of reasons why a kid doesn't "show what he's capable of" and I would go with your gut feeling about it -- i.e., whether it is consistent with his temperament or a possible red flag for something else. With my DS6, it's the latter, because he's very vocal and unreserved (maybe even competitive) when he's engaged in his learning. His K teacher telling us that he doesn't show what he knows was one of the first warning signs of him being underchallenged. He tends to become gun-shy about trying new things and taking intellectual risks when he gets too used to never getting anything wrong. So for us, this type of thing is a sign of perfectionism that goes away when he gets more challenge.
