EVERY YEAR, the College Board collects and publishes information on the last group of high school students to take its best-known test, the SAT. And though the students in this snapshot are no cross-section of the population -- college-aspiring seniors are "self-selected," as they say -- such a group snapshot puts things in some much-needed perspective for policy makers. SAT scores overall are no longer dropping, and that's good news. But what put a stop to the scores' 10-year slide and what that should mean for policy are more complicated questions. No one, after all, could ever agree exactly what was causing the drop in the first place.

One thing is clear: part of the halt is due to the improved performance of minorities, especially blacks. White students' scores are still sliding -- they dropped two points in the verbal section between 1985 and now, and one point in math. Black scores, by contrast, went up five points on the verbal section (out of a possible 800) and one point on the math section. Overall, black scores over the last decade have gone up 42 points, though they are still well below those of whites. (Readers ought to note that this newspaper owns a company, the Stanley H. Kaplan Educational Center, which coaches students for the SAT.)

The obvious temptation is to point to such gains as evidence that this or that education reform initiative is bearing fruit. But things don't happen so fast in education, and the scores earned by high school seniors, in particular, tend to reflect long-term cumulative changes that began taking effect when the seniors in question were elementary-school students. That proviso means -- as a recent Congressional Budget Office report on test scores makes clear -- that, contrary to popular belief, the long decline of test scores throughout the '60s and '70s probably did not result from the same years' drop in prospective teachers' own test scores, or from overly "progressive" federal education policies that turned the curriculum gooey. That's not to say that these trends didn't do damage, but simply that that damage is not what we're looking at; and, also, that the more recent upturn in both SAT scores and scores among younger children may also have its roots in some policies of those now educationally unfashionable years. Compensatory education funding for disadvantaged children, for instance, passed Congress in 1965 but didn't really get rolling until the early '70s, when last year's high school seniors were in first grade. Similarly, school desegregation in the '70s may have helped raise the aspirations of black students. (It's likely, though, that the more substantial reason for the rise in black scores is that more black families have reached a level of affluence where they can live in better neighborhoods and send their children to better schools.)

It is an irony of score evaluation that when larger numbers of students overall aspire to college, and therefore take a test such as the SAT, that group tends to include larger numbers who don't do well. Because of this, average scores go down, at least temporarily. Eighty thousand more seniors took the SAT this year than last year. That tradeoff may be leading to the score plateau among non-minorities, but it is the kind of change that pays off in the long run.