I believe this is true, as a general statement: "the average high school student is an incompetent writer." I believe it, because as a father of two kids I've experienced the "quality" of the American public school system firsthand. I've also noticed a marked decrease in quality since moving to California from Illinois--the latter isn't great in this respect, but it's certainly better than the former.
Schools like the VanDamme Academy in Irvine, California are priceless. I only wish it weren't so far away.