U.S. colleges of education are an "industry of mediocrity" that churns out teachers ill-prepared to work in elementary and high-school classrooms, according to a report by a nonprofit advocacy group that represents the first comprehensive review of such programs.

The study, by the National Council on Teacher Quality, which has long promoted overhauling U.S. teacher preparation, assigned ratings of up to four stars to 1,200 programs at 608 institutions that collectively account for 72% of the graduates of all such...