Educational Research & Information Clearinghouse
ERIC, sponsored by the U.S. Department of Education, Institute of Education Sciences (IES), provides free access to more than 1.2 million bibliographic records of journal articles and other education-related materials and, if available, includes links to full text.
The Eisenhower Clearinghouse specializes in math and science. Its criteria are explicit and input is sought from several classes of users, though not always consistently.
Since the holdings in these clearinghouses are so vast, preparing a list of key words for a search or formulating questions ahead of time will save time.