A good backpack rule is simple is usually better and worth any amount of money. I was a teacher and I actually carry backpacks often.
I never carried a backpack until college, got a inexpensive one and it died about a year in. Then I bought a black denim fabric backpack for about 20 bucks. Expensive at the time, it was just one big pocket with a small pocket on front that was about a third of the size of the front of the backpack. It lasted 10 years (I carried my backpack everyday instead of a purse while working, attending school, and teaching after college) after that I replaced it with another. Same brand same fabric except in blue denim and I've had it for about 6-8 years. I didn't bring it with me today but I don't think it's a Jansport, it is however one of those common name backpacks that escapes me at the moment. I actually used it in WDW last year (I do have a bagalini but I wanted something with a bit more room). It was great.
Avoid a million pockets, get a sturdy fabric and buy from a name with a good rep. Even at twice the price this is an investment that usually pays off.