A number of states have embarked on ambitious programs to reduce the number of students in classrooms -- believing this to be a panacea for poor student test scores. But a recent study by Eric Hanushek, a top education economist based at the University of Rochester, suggests that smaller classes don't necessarily mean greater student achievement.

In "The Evidence on Class Size," Hanushek surveyed 277 studies that attempted to correlate student-teacher ratios and student achievement.

• While pupil-teacher ratios were falling nationally by 35 percent from 1950 to 1995, performance indicators such as scores on the National Assessment of Educational Progress did not go up.

• Six international tests in math and science given between 1960 and 1990 show some correlation between larger class sizes and improved performance.

• The state of Tennessee's 1980s experiment with class-size reduction -- which compared smaller kindergarten through third-grade class sizes (13 to 17 students) with larger ones (21 to 25 students) -- showed some improvement in kindergarten children's performance, but none among students from the first grade on up.

The route to performance progress seems to lie not in reduced class sizes, but in an increase in teacher quality.