I think the regression and forgetfulness comes along when a kid who can do math in his head with no particular thought for the process is suddenly faced with thinking about the process. Do you know the story about the caterpillar tying his shoes? It's like that--you can't stop to think about it or you get confused! There's also the fact that the methods taught often don't correspond to the method that has been working fine in the head, and often the teaching pushes that method as "the right way" and suddenly the other way is "wrong" so they stop it.
Yes, six year olds are supposed to be emotionally immature--and highly intelligent ones are even more so if they are expected to sit still and do stuff they did when they were two. To paraphrase what someone said a while back, if you made a sixth grader sit down and do first grade work, he wouldn't behave well for long, either. I hope you can get the school to reconsider that "emotional immaturity" thing and start getting him some higher-placed education instead. Hang around here and learn from the masters--there are some people who are truly gifted at advocating around here!
