It was a gradual decline over generations, but in the year 1900 most schools were fine, by 1950 basically all schools had been taken over by leftist machines. As others in the thread have pointed out, Rockefeller had a lot to do with that progression.

The one room neighborhood/home school, run by one of the neighborhood mothers or grandmothers, was fine. Centralized schooling, where hundreds or thousands of children are gathered together, separated by age, taught standard curriculum decided by committee, by teachers trained in marxist universities, is an unmitigated disaster.

And not just because the teachers are marxists, simply gathering that many children together is a disaster. Instead of the natural hierarchy of age to organize the children, they are segregated into massive same-age groups, which is completely unnatural. From this perverse situation, negative behavioral contagion is amplified, hierarchies are built upon bullying and sex appeal, and children learn horrible lessons about how to succeed and their worth in society. Add in the marxist authoritarian teaching and there's no where to go but down the drain.