Textbooks weren't always as big as they are today.
And I don't just mean history textbooks. Sure, there's more history today than there was when I was in high school, so maybe history books need to be thicker. But English grammar and composition hasn't changed that much since the early 80's, and high school-level math hasn't changed at all.
So why are the books so huge nowadays? Why are teenagers' backpacks tearing from the weight of the books?
I'll tell you why. It's because publishers (and others) think teenagers are stupid. They absolutely *cannot* do problems unless there's a marginally-related picture nearby to draw their attention. They absolutely *cannot* read unless their eyes are focused on the page with a one inch border of empty page around all the type, adding several square inches to each page and cubic inches to each book. And why does every problem have to be about buying CD's? Don't kids buy anything else? Or can't they understand anything but buying things?
The textbook should be a tool. Whether the teacher chooses to amplify what's in the text or to have the text complement classroom instruction, the text should not be a mixture of academics and entertainment. Neither should it insult the students by implying that they're not capable of taking their textbooks seriously.
Instead, we give them books that are easily help up to mockery--if the kids can lift them. Backpacks are too heavy. There isn't enough room in lockers.
Entire forests are being clearcut for these tomes!