Your description of your son's experience in school could be my daughter's, except at her school they don't even have a gifted program!
They came back to me and asked for more for the portfolio, and I had included worksheets that seemed to be several years above grade level. I spoke with Rebecca extensively, and she suggested video-taping my daughter doing some worksheets or puzzles and talking through the process. What they really missed from the worksheets, I think, was the metacognition and process.
