My son goes to a Mathnasium. It's been wonderful for him. They have their own curriculum, and it's mathematically correct. I vaguely remember hearing something about the Common Core from the guy who owns our local center, but I'm not concerned about it either way because of the fact that their curriculum is mathematically correct (the lack of this trait was what the CC was designed in part to address).
Each Mathnasium is individually owned, so the quality and approach at each one presumably varies. That said, and FWIW, they're very much unlike Kumon. I would just book an appointment for them to test your son and talk to the director about what the center can offer him.
