Seems John Baylor (of the ACT Prep course) agrees with me. Here's a paraphrase of what he says.
High school kids need to read AT LEAST a book a month during the summer. During the school year, in addition to reading ALL the assignments, they need to read at least book every other month. (That amounts to about 6-7 books on their own every year.)
"You'll never be penalized in your life for not having gone hang gliding or rock climbing or skiing. However, I guarantee you will be penalized on the ACT for not reading!" John Baylor
So listen to John Baylor! Go Read!