I once knew a very bored elementary student who couldn't sit still, look like he daydreamed sometimes, doodled, and didn't even once glance at the teacher while she was instructing and he was able to get his work done as expected and properly. My guess is that he was highly auditory and had very good perception skills to where he didn't need visual input to "get it".
Is your son still following what is expected in class? Do you think he needs more challenge (not a new lesson but more complexity to his work)?
One way I extinguish whining is to pretend I don't understand a thing.... like he is speaking a strange foreign language. When my son uses his "talking voice", I pretend I clearly understand what he is saying now and very relieved.
How about a stress ball while in class?
