I also think it is worthwhile to consider taking the child out of K this year, skipping K and putting him in first grade next year.
Ours had problems at 4 that sound similar. She didn't act out, she withdrew (while smiling on the outside). Her personality at home changed so much we thought we had lost our child. The school said she was happy, but when they filled out evaluation forms for us, they noted autistic-like behavior, so there was a mismatch between school behavior and the school behavior that was reported to us.
Unlike HowlerKarma's daughter, mine really did need out of the situation. grades or work offered or any of that stuff wasn't even a consideration. We just needed her out of an atmosphere that had become toxic for her. When we removed her from the atmosphere, things were immediately better.
We did things that I wouldn't recommend to you--and mine has problems that you don't mention. However, I will say that I do sometimes regret not having her skip kindergarten and go straight from preK into first grade. Kindergarten is about writing and drawing, learning the rules and learning the alphabet. I think if you are thinking at a much higher level than your output allows for, kindergarten can be a really frustrating experience. No play, no thinking, lots of drawing and writing.
