I think first grade is a particularly tough year for these HG+ kids. I hear it often from the personal experience of people on this and similar forums, saw it with my own DS, and have read that it is so in various books and websites. First grade is a sea-change, I think, and it tends to show the problems with trying to fit our kids into an educational system that isn't made for them.
The teachers make all the difference! If I had DS6's first grade year to do over again, I'd have moved heaven and earth to get him into a classroom with a good teacher for first grade. As it was, I didn't know the one we got wasn't good. I didn't ask the right questions of other parents and of administrators. (Heck, I didn't even ask what his test scores were! Duh!) I went with the flow. If I knew then what I know now...
I'd make waves! Big, gigantic crashing waves!!!
