Found an article on a local student-run survey of students and teachers in the Providence schools. Here's their web page.
When asked “I spend most of my time
in class working on dittos”, 83% of
students answered Always, Often, or
Data was similar for the question “I
spend most of my time in class
reading the textbook on my own”, with
71% of students answering Always,
Often, or Sometimes.
But did they ask how many students read the textbook before they come to class? Can you tell I'm having trouble with my classes not doing the reading again? ;)