Here's a brief roundup on choosing a school.
- The Davidson database has information on choosing a school, including Choosing the right school for your gifted child (contains "must-ask questions and the answers that you should seek")
- Dr. Donald Treffinger's list found online at the website of Center for Creative Learning (CCL), and called “Dear School People”.

Will your child be grade-skipped 2 years and accelerated in math 4-6 years, when beginning this potential high school placement next year or the year after? As your child is currently homeschooled, you most likely did not go through a formal process prior to accelerating. However, prior to contemplating placing him in a brick-and-mortar school several grades accelerated, you may wish to review the Iowa Acceleration Scale, to ensure that you have given thought to a wide variety of academic, intellectual, and interpersonal factors which are important for classroom success after acceleration.

You might want to ask the school the number of other students they've enrolled with multiple full-grade accelerations... as well as the number of students for whom they've made advanced curriculum available. Essentially you would like to verify whether your son is likely to have a cohort of academic/intellectual peers? Chronological-age peers? If he would be boarding, you may also wish to ask about dorm rules, roommate assignment, processes/procedures for roommate incompatibility, etc.