My daughter went to Boone Preschool and we LOVED it. (4th & Douglas in LS) She went from age 2 until starting Kindergarten at age 5. The first three years, she was in the daycare program (my husband & I work full time), and then the 3rd year she went to the preschool program (and went to the daycare before & after the preschool hours).
I can't really speak to just the preschool program, because she was learning also in the daycare (they have a set curriculum too), but she was more than ready for Kindergarten. I would say the first half of Kindergarten was a review of what she'd already learned at Boone. And the thing I liked best about the daycare is how involved the teachers are with the kids-- we toured several places before we decided on Boone, and at most of them, the teachers sat apart from the kids either talking to eachother, or just watching the kids play. At Boone, the teachers were down on the floor interacting with the kids.
Another thing I like about Boone is that it is so individualized. The teachers really know the kids and their abilities, and they don't "move them up" until they're ready. Moving up is not automatically based on age, as it is in some programs. Again, I'm not sure if this would really apply to the preschool if you're only going for one year, but it kind of gives you an idea of how they treat the children as individuals.
Good luck in your search!