Junior, did your son have a cognitive (IQ) test done as well? I would hesitate to skip a child 2 full years this early in the game unless that half of the equation was equally strong. Even then, I'd probably suggest a more gradual approach, such as Cathy's son has experienced.

We started our son in K at 4.5. He is now up 2 full years and more in his best subject, but no single skip exceeded one year. It's been a very gradual process.

If your school is willing though, it might be worth considering. At a minimum, try for the early K start with subject skips or serious differentiation in the more basic subjects (reading/math). It's unlikely that the single skip alone will be "enough" on its own with scores in the >99.9th range.

I suggest you visit the kindergarten and see what it looks like. DS and I visited in the spring and met both teachers and felt quite comfortable with him going there. Maybe it's too late, though, for you to visit. At least try to meet the teacher and get a tour and find out if he/she will be flexible for kids that aren't in the middle.

Ditto what Kriston said. Kindergarten can be more fun and a good time to bond with school and learn basic school culture and rules. First is often very regimented as there are standards that all kids need to meet, which means that the teacher is forced to focus on the kids who are having trouble making those standards. But each school and kid is different.