I don’t know if this is what you’re looking for -
http://www.hslda.org/docs/nche/000000/00000017.asp
It’s about halfway down the page. (How Are Homeschoolers Scoring on College Entrance Exams?)
....In math, homeschoolers scored 19.2 compared to the national average of 20.2....
How do you reconcile that fact to what you think is true?