uh, yeah - if your little dude is PG... i dunno - my kid is nowhere near PG and we've had to accelerate her by 3 years in math - and she's not even breaking a sweat - i expect she'll hit the next grade's material by sometime in october.
but... that said, she had the exact same issue in school last year. anything that she didn't do instantaneously in her head felt "too hard" - so basically the only thing got out of school last year was a wicked case of perfectionism. i am working on de-programming her, but essentially she came away thinking that "learning" was equivalent to "showing what she already knows." yikes.
i think the trick is to get them to feel like that uncomfortable, wrong-footed, icky feeling is desirable, because that means they're actually learning something... the trick with your PG kiddo will be finding anything that challenges him AT ALL. all the best - sorry i don't have more advice, but there will be a ton of people here who will have blazed a trail for you!
