THE MAIN thing to keep in mind about the Education Department's latest back-to-school statistical report, which notes a continued rise in both spending on education and school enrollment, is that it assumes that no education reform of the past few years has worked. That is because the report is based on trends and policies up through 1988 and on patterns projected from them. The trouble is that the statistics paint an education picture a good deal more stable and serene than the reality.

In fact, the last two years have been anything but stable for spending on education. The changed economic climate has led many strapped cities to scale back on planned hikes in such spending and, in some cases, to cut it outright. That's a reverse in the widespread education increases that shaped the projections in the Education Department's report. Some of the good news in the report is true: for instance, teachers' salaries on average are way up, a long-overdue improvement and one that should pay off directly. The '80s brought the profession's salaries up as much as 23 percent. Some bad news hides in the spending trends as well: higher spending on college and university education, for instance, mainly reflects higher tuition prices, which public and private financial aid sources have tried but failed to keep up with. (College costs more than doubled during the 1980s, the College Board reports.)

None of this tells us whether education reforms are working, or whether, if they are, it was spending that made them work. What it does tell us yet again is that our methods of gathering data to answer those questions are inadequate, that they tend to fall out of phase with the current realities and that what we really need is a decent measurement of what's coming out of the schools, rather than just what's going in.