Public education K-12 has deteriorated drastically since late-1960s-1970s. Decline has severely accelerated since the 1990s, as standards have been watered down, plus so much money is diverted to education of massive numbers immigrants & illegal aliens - starting with English as a Second Language programs, but much, much more. Social promotion is the norm instead of requiring specific performances at each level. Thus many HS grads are near-illiterate, near-innumerate, & woefully under-educated.
University education still ranks well overall worldwide since there are many excellent universities. Many of the world's top 10, top 100 & top 500 universities are US schools. Of course, with over 3000 colleges & universities in the US, there are those among the world's greatest universities, and those near-worthless, not even ranked internationally. US has a far wider variety of schools & school-quality than any other country.