The IHSLA did a fine job of managing boys lacrosse for years - 2 divisions, A and B. The playoffs were based on power rankings and typically held pretty well for the post-season (full details can be found at the link).
http://www.ihsla.org/Standings.aspx
At the risk of making this a private vs public discussion, which is not my intent, it is my impression that the IHSA allowed public school co-ops to continue this season, but that is not allowed for private schools.
Are there other sports that have co-op teams competing?