I remember reading in the paper a few years ago that OK had one of the highest SAT average scores. The reason is that most out of state schools require SAT and not ACT so the logic is only the kids going out of state are taking the SAT and these kids are typically more affluent, better educated etc. Not sure if this translates to home school as well but might explain some of the reasons that the home school ACT numbers are so low. I don't have time to look this up to be sure, just an idea.