But many times in my career as a student I felt like I was one of the few who came to class having read the material that was asked to be read (speaking of undergrad and graduate school college level here). I assume many people read the book but not necessarily on the time schedule requested. If you asked students to read the material AND watch a lecture before class...I can only imagine that I there would be even less who had done the all the prep work.

...reading is pleasure, not just something teachers make you do in school.~B. Cleary