<p>If it were my kid, I would have told her to go to one of the schools she got into, do really well, and then decided if she wants to transfer. By doing well in college would give adcom another (better) datat point.</p>
<p>At D1’s high school, few kids every year would go to a highly ranked boarding school for another year and to re-apply again.</p>
<p>I also second the suggestion of working with a private counselor to see how OP’s son could improve(change) his application, and what he could do during his gap year to make him a better applicant.</p>