What major changes happened between 1940 and 1970 for education?

Well, that's a thirty year time period, and a lot happened
in those thirty years, so it's hard to say if this is the information you are looking
for.

I'll concentrate on two major changes.  In 1954, the
Supreme Court ordered schools to be desegregated.  The government enforced the ruling
and across the South, schools were forced to open their doors to black students as
well.  By 1970, that process was largely complete.

After
Sputnik, a Russian satellite, was launched in 1957, the US passed the National Defense
Education Act, which changed all of the graduation requirements, placed an emphasis on
math and science, and created the AP program.  High school moved away from basic job
preparation towards college preparation.