I used to have to do that, too. Everything, including workbooks, had to be covered. I usually used contact paper on the workbooks (which was ok because you just threw them out at the end of the year). For textbooks, I used either brown paper or store-bought book covers. My high school also gave out book covers with the school logo and a bunch of ads; I used those during HS, taking care to fold them so I wouldn't have to look at the ads all year.
I remember that one year my mother found these really nice transparent book covers. I nearly got detention because my teachers didn't believe I'd covered the books.
Threaded Mode