Because so many responsibilities are heaped upon them, public schools get a lot of attention - and a lot of criticism. So much criticism, in fact, that it's easy to conclude American schools don't do a very good job.

This impression, however, is way off base. Just how far off is indicated by a new study last week from the Rand Corp., a highly respected and widely admired think tank in Santa Monica, Calif.After studying various surveys, including the test scores of students who took the National Assessment of Educational Progress examination between 1970 and 1990, the Rand Corp. concluded that U.S. schools have made decided progress over the past couple of decades. In fact, we have some of the best schools and smartest students of any industrial country, no apologies to Germany and Japan.

Among other achievements, the Rand report cites:

- Student math and reading performance improved for all racial and ethnic groups between 1970 and 1990, with black and Hispanic students making the most significant gains.

- Money spent on compensatory education and equal opportunity programs has not been wasted. The gap between minorities and other students has narrowed, though a gap still exists.

- The fact that helped most is better-educated parents, who are able to give students more help at home.

Like many studies, this one isn't perfect. It concludes, for example, that poverty, not single-parenthood, often leads to poor performance in school. Since single-parenthood is a prime cause of poverty, it's a distinction without much difference.

Nor should Americans pretend that all is well in education. Students in suburban schools - if they have rigorous standards - tend to score higher on tests than less-fortunate children who live in congested cities, where resources are fewer and entrenched bureaucracies resist change.

Schools in some hardscrabble rural areas can be pretty dreadful, too, which is why states should make sure that every district has at least a minimum level of quality education.

But the notion that public schooling is inherently inferior never was accurate or fair. The fact is that the best students at public schools are excellent, and some of their slower classmates are rapidly catching up. For this achievement, take a bow, teachers - and parents, too.