WASHINGTON, D.C.: Happily, just as in Lake Woebegon, America's fourth-graders are above average. Unfortunately, it may be all downhill from there, and that suggests that something is wrong with American schools. In the Third International Mathematics and Science Study, American fourth-graders ranked third in science (behind Korea and Japan) and 12th out of the 26 countries in math. In another study last year, U.S. eighth graders finished 17th in math and a woebegone 28th in science. The fact that younger students compare more favorably than older ones suggests that American schools may be slowing them down. Education Secretary Richard Riley says thatís precisely why President Clintonís proposed national testing standards are so desperately needed. "Our elementary schools are getting better at teaching the basics," he said. "Our goal now is to keep up the pace and make sure that they are learning to these high standards all the way through to high school." But at an estimated cost of $10-12 million per year, the proposed tests will be a hard sell with Congressional Republicans and others who oppose standardized tests.