The high school I attended sent about a third of graduates to four year colleges immediately thereafter (additional graduates went to the local community college). Most of the colleges were in state publics, but some privates were represented.
Test prep certainly existed, but did not seem to be done to the intensity that seems to be the norm now.
These were not that many AP classes, and it was not the norm to take all possible non-foreign-language ones plus the foreign language of your choice.