You are right to pin the blame on Dewey, but that means the rot did not really begin in elementary and secondary schools, but in colleges of education where Dewey's baleful ideas (and in later generations Vygotstky's "social construction of knowledge") were taught, and in the state legislatures that gave colleges of education a monopoly on producing "qualified" or "certified" teachers (or whatever other term the particular state chose).
When my father went to high school in the 1940's his teachers didn't have degrees in secondary education, they had masters degrees (or in a few cases PhDs) in the subject they taught.
Now it's ed majors from K through 12, all formed with Dewey's "progressive" ideals and worse, and about 85% of whom picked their major because it was the easiest one offered at their university. (I choose that figure from the experience having taught "Math for Elementary School Teachers" a few times -- a class in which, despite being taught in the Department of Mathematics and explicit warnings in the syllabus and in class that it is a course on mathematics, not mathematical pedagogy, a sizable percentage of the students are so stupid they complain that mathematicians are teaching them mathematics, not "how to teach math".) Secondary ed majors are a little better, but not much.