K.C.
I know you've already received recommendations for DKH Academy in Highland Village, but I just wanted to say that we absolutely loved it! My son went there for 3 years (3-yr old, 4-yr old, and Jr. Kindergarten). The staff is awesome and I always highly recommend them to everyone!
My son's birthday is in August, and we also thought he wasn't ready for the long kindergarten days, so DKH was the perfect solution at 1/2 days.