I'm a high school teacher at a public school, our kids don't buy textbooks - we supply them for the lesson and (in my subject) they stay in the classroom. So they don't have the ability to write/highlight in them anyway. I wouldn't think they would really even need to until senior years anyway.
Wow. That disturbs my brain. I can't get my head around not owning my own text book, let alone not having a need to study it until senior levels. LOL