Except for one thing ... Schools tend not to fail many people. When an entire cohort has a different level of ability, standards adjust. Possibly some proctored, standardized exams might be more comparable over time. I have read that, controlling for student demographics, SAT scores (frequently used for US college entrance) were increasing until the mid 2000s and then flat since then.
Yes that's always true for the preceding school, but it really only means that the student needs to work harder or fail later on as the final job enabling exam isn't going to move.