Many good suggestions—a junior boarding school because they have connections to the high school boarding schools and support him in finding the right fit; and hiring a consultant—expensive but typically there are different levels of service do even creating the best fit school list would be worth it (if you do it now they could also guide you to schools that might have post A10 spots). And I agree—if the LDS would be new to him, you’re not interested in a junior BS and he’s set on finding a BS for the remainder of HS then I’d consider keeping him in his LPS with his friends for consistency as long as he’d be challenged academically, has good EC opportunities, etc.