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.
