Imo it should be the school's responsibility to stick a notice on the classroom itself or at least send an email, rather than expect each and every student to check an app every day. I hadn't been a high school student in a while through.
I agree that there should be a physical fallback or sorts, but I think it's helpful to be prepared just in case. If the school is too lazy to display schedule changes at school for some reason, the app becomes a necessity and that's just stupid.