Granted I've been out of school for decades. The textbooks were always an accessory to classroom instruction and not intended for stand-alone learning. Math students quickly figured out that the most important thing was doing the problems, the text was essentially a reference, and the classroom was for guidance through the concepts, and for motivation.

Of course the humanities classes were about books, so learning how to study the books themselves was a major part of the practice.

Programming seems to lend itself particularly well to self learning because the computer allows for endless trial-and-error practice.