Hello,
Centereach is part of the Middle Country School District. Universal Pre-K & Kindergarten are held in the same buildings (Bicycle Path School or Unity Drive School). Kids then go to one of the school district's 8 Elementary schools for grades 1-5 depending on where you live (you can contact the registration office at Middle Country and they will tell you which one you're zoned to).
They do offer before/after programs through the Selden/Centereach Youth Association, however these are independent of the school district and charge a small fee. They are held in the individual schools however. This is their website:
E-pre-K-BandA
Good luck. We like the district, my kids are happy there.