I think at that age, it's about following directions and staying engaged. Mine (now in college so long ago) was not given a choice but to skip K. They thought she was mature because she loved school-- I thought emotionally immature due to strong temperment, but learned that it was mismatch, not immaturity. Immaturity was another student who was skipped and used to wander off, couldn't follow the class in line, and couldn't start desk work without someone standing over 1:1.
How is the academic fit? Size? Athletics?
I think it's really hard as a parent to skip a kid this young. We may desperately hold onto a "normal" life. If you look at kids your son's age, do they look like babies to you? (when mine was in 4th grade, I couldn't imagine her being in 3rd with those little kids).
