In general, the schools in the metro west area have the highest test scores and best track records all the way around. Newton included.

Concord is an excellent system. Lexington has good programs if your child can be in an inclusion situation, but they are rigid about providing services outside the classroom and district and they have relatively large class sizes which can be problamatic. Weston is an expensive and affluent town with excellent services. I have not had direct contact with Westford, but overall have heard positive things.

North of Boston I'd stay away from N. Andover, Pentucket Regional. Andover, Boxford and Topsfield are pretty good.

I'm not familiar with towns south of Boston.