I would definitely advocate for an accelerated course in the 2nd grade stuff and then moving on. We have had similar problems with teachers either not understanding how he learns or focusing on him proving HOW he knows what he knows. My son is not PG, but MG/HG (still some confusion about that), but his math-related ability and achievement scores are much higher than his verbal. This year he skipped from 2nd to third and is excelling in the math at the 3rd grade level (even though he was only in 2nd grade math for two months and therefore missed most of it), which of course is too easy for him. His achievement tests placed him at an average of 7th grade, 9th month for what he already knows. He has a lot of trouble with "show your work" or "explain how you figured this out" questions. He just knows. For example, he had homework this week which consisted of taking square tiles and experimenting with them to create shapes with certain perimeters. He was supposed to draw the final shape and explain how he came up with one with a perimeter of 10, using 4 square tiles. Well, he didn't use the tiles. He literally read the problem, sat down on the floor, and immediately drew a shape which encompassed four squares and had a perimeter of 10. What I don't like is that they have gotten on his case about explaining his thought process, and he really CAN'T sometimes, so he lied on his homework. He said he experimented to see how to make the shape, which is patently false. Ugh. Going to have a talk with the teacher to see if this can be sorted out. I don't want my kid lying about anything just because adults don't understand his abilities.
