When I was at school I always had LLBean bags. I can't remember how many I got through, but the last one, that saw me through A-Level, and may have been used at GCSE too, proceeded to see me through five years at university, and a further 12 years as my daily go-to-the-office bag. It wasn't a laptop carrier, and was a top loader so didn't have the same issues with zip failure that panel loaders can have, but still, it did very well. I still have it, I could still use it, providing that I don't mind about all the urethane laminate having flaked off the 500d Cordura many years ago.
When one is no longer throwing ones bag down as a goal marker at break, or having it kicked about, or over stuffing it with books and football kit, bags can last really well, even when they are far from a premium brand.