I like how Louisiana does it. They have select (schools that can pick their students - magnet, private, charter, football academies like John Curtis) and non-select (district-based admission) divisions in the playoffs. However, during the regular season the divisions are based on student population/proximity to one another. So, you end up with divisions where private schools actually play the public schools nearby if they're comparable sized. For example, Mandeville HS's (non-select) biggest rival is St. Pauls School (select) - they play in the same division, but they don't compete in the same playoffs. It's a lot less travel for the schools and makes for some intense rivalries.