A lot of high school English teachers assign summer reading, which might be worth it if all the students came into the new school year ready to discuss the reading. The reality is though that they do not.
I am not a fan of summer homework assignments, as I also think kids should read what they want in their down time. I also believe that parents should be a major player in their child's education. That said, parents should decide if they need to take another trip to the library, museum, historic site, etc. I agree with another commenter that experiences are good for learning also. Not every learning experience needs to be an assignment, and giving children the summer to explore and think out side the worksheet will teach them to be life long learners.