As this strip indicates, John says he is against April's graduating from eighth grade to the freshman year of high school (or, to put in in Canadian English, from Grade 8 to Grade 9) because he doesn't believe the transition from middle school to high school is especially worthy of attention. This is very interesting and very telling because the whole "in my day" experience is pretty much a dog-whistle sort of deal.
This is because whenever someone runs his mouth about how things were different in his day and children weren't so soft and didn't have so much handed to them because it makes them ungrateful, what's really going on is that Daddy hates the fact that he didn't get a party when he was a kid and can't abide the idea of someone getting something he wasn't allowed to have. He poses as a guardian of the traditions but deep down, John is a mean-spirited child mewling for toys he cannot have. The sad thing is that he achieves the near-impossibility of having less self-awareness than Jerome "It MUST be the PC police hounding me because the scary alternative is that I was never all that funny to begin with" Seinfeld, Esquire and thinks of himself as an exemplar of common sense.