100 years ago, the parents were in charge of their children’s education. No the schools are run by bureaucrats, unions, and government certified teachers.
Because large rafts of education is now under the control of the state, its provision and effectiveness become a valid political point. Now, no elected official is going to want to lay themselves open to a charge of "letting the kids down" by poor education, so there is a built in bias to see "improvements", in financial provision, attendence, and (especially) exam results.
Now, theres only three ways exam results can continously improve. Either 1) children are getting smarter, or 2)Schools are getting better at teaching or 3) the exams are getting easier. Care to place a bet on which one it is? Hint, the last option is by far the easiest and cheapest to do.