NEW YORK—The ideal size for a high school is between 600 and 900 students, according to a University of Michigan study presented here today (April 10) at the annual meeting of the American Educational Research Association.

“Students learn less in small schools,” says Valerie E. Lee, associate professor at the U-M School of Education. “And in large high schools, especially those enrolling over 2,100 students, they learn considerably less.”

The effects of high school size on gains in learning are greater for math than for reading, according to Lee.

“Moreover, size seems to matter more for some students than others. Size is especially important in schools attended by the most disadvantaged students,” she says. “In schools enrolling large numbers of minority and low-income students, learning falls off sharply as the schools become larger or smaller than the ideal.”

The study by Lee and Julia B. Smith, University of Rochester assistant professor, was based on data from nearly 10,000 high school students in 789 public, Catholic and elite private high schools, collected over four high-school years. “Learning” was measured as a gain in achievement over that period.

For the study, Lee and Smith used a sophisticated statistical analytic technique called hierarchical linear modeling (HLM) to examine the effects of school size on gains in learning for students of varying socioeconomic, racial/ethnic, gender and ability backgrounds in public, Catholic and other private schools with varying percentages of minority enrollments and socioeconomic compositions.

Most high schools should be considerably smaller than they are if the nation wishes to maximize student learning, Lee and Smith conclude. Very small high schools, as well as very large ones, are also problematic, even though learning is more equitable in small schools.

“Minority students are particularly likely to attend large schools,” Lee notes, “and students of lower social class are likely to be found in either large or very small schools.

“The issue of school size is much more important in schools with high concentrations of low-income and minority students. Thus, schools with many minority students, and those with many students from lower-socioeconomic status families (often the same schools), should be especially anxious to reduce the size of the units in which their students actually learn.”

The researchers mention establishing schools-within-schools as one way to accomplish this task without large additional expense.