Prince George's County public schools Superintendent John A. Murphy has released statistics that say black students, as a group, score more than 20 points lower than their classmates on standardized tests. The figure can mislead. It blurs the fact that, among black students or any students, there is a range of achievement that goes from very good to very poor.

Prince George's County educators have been studying the performances of minority students, but their work is far from done. More complete statistics would show where black students perform well and why, and how many perform poorly and why. But even without that information, important points can be made.

It is a commonplace to say that students from low-income homes with little money for educational resources will not usually perform as well as more affluent children, whether they are black or white. A lack of proper adult role models is also a factor. It is less common but equally true to say that those factors can be countered by successful schools. Mr. Murphy is following "the effective schools approach." That means a strong principal, an eager staff of administrators and teachers, effective outreach to involve parents, frequent acknowledgment of successes by students and high expectations.

Such a model already exists in Prince George's: Concord Elementary School in District Heights. About 86 percent of the students are blacks from low-to low-middle-income families. Principal Joyce Dandridge sends her highly motivated staff to visit parents. She checks homework and tells parents that they must sign their children's homework to be certain it has been done. She has students, parents and teachers sign "contracts" in which the students promise to study every night. She rewards good studen performance in several ways: by awarding pins and buttons, by putting their pictures on a "student of the month" bulletin board or by making them officers in her "Principal's Army." And Miss Dandridge is very strict about attendance.

The results are striking. Concord's predominantly black fifth-graders, for example, scored at the 76th percentile in the most recent standardized tests, 18 points above the school system's average fifth-grader and 26 points above the national average for fifth-graders.

Such performance dispels the myth that black students from lower-income families cannot achieve academic excellence. If the county can achieve such results in one school, there is no reason to believe it cannot happen in others.