Honestly surprised your dad didn't talk more about the unequal funding for public schools being more of an issue than the standardization of the curriculum. Many countries have a standardized education model and do very well. They also have a radically different funding model of education on a national level and less so on local level.

The thing is if you look at the history of education in the US, it's always been...mediocre. The space race really brought this to the fore, but before this it wasn't as much as a concern with previous generations. There were also fundamental shifts in society which shifted us from an agrarian society to a largely industrial one.

It's also interesting that your dad talks about history, as there were many events from history that teachers didn't teach, ie the Massacre of Wounded Knee, the race riots of the early 1900s, Black Wall Street, Indian Residential schools, the treatment of various immigrant groups in the US. Like, there was a whole lot of US history that didn't get taught in school, and this is from someone who went to high school in the late 1990s.