The Sage School in Foxboro, MA is the place. Others are either just starting, not complete in resources, or curriculum and frankly, not worth my money. Sage on the other hand, has been around about 25 years, is Pre-K through 8th grade. The curriculum and the teachers are what makes this school shine. A must for academically gifted if you truly want a "gifted education" without homeschooling. They understand the needs, no more explaining, offer music, art, latin, spanish, dance/movement, etc. and of course their mainstay-the academics. Your kids will learn how to write while studying history, learn how to think and work in groups. There are two teachers to each classroom, not a main teacher and a subordinate, but two real gifted teachers per classroom. The classrooms have low numbers, so the intensity of the curriculum and activities is high. It was a perfect match for my gifted kid. What I think that I can say to any parent with a truly gifted kid is that my kid is excited every day to go to school, he has a great time, and really enjoys school. He already enjoys learning, but as parents, we appreciate that Sage School has kept the spark alive for my son.
Good luck with your search.