The study, to be presented today to the American Educational Research Association meeting in New York, found student achievement declined in high schools with enrollments outside that "ideal range."
"That they could set an optimum range is particularly meaningful," said Michael Heim, director of the state Department of Education's planning and evaluation branch.
Heim's own 1992 analysis of Hawaii's public schools concluded that smaller schools tended to be better than larger ones, but he couldn't determine an optimum enrollment.
For the study released today, researchers at the University of Michigan and the University of Rochester charted the progress over four years of almost 10,000 high school students in 789 public and private high schools.
Pupils in schools with 600 to 900 students showed the highest reading and math achievement, regardless of whether they were well-to-do or poor. Achievement declined in schools smaller or larger than the "ideal."
Students did worst in high schools with more than 2,100 pupils, the study said. Very small high schools also hurt learning.
The average public high school in Hawaii enrolls about 1,300 students -- 90 percent higher than the national average. Meanwhile, Hawaii public schools students on the whole tend to score below the national average on tests such as the Stanford Achievement Test.
Among the 23 Hawaii public schools with grades nine through 12, only one, Lahainaluna on Maui, has an enrollment in the 600 to 900 range lauded by the study, according to enrollment logs. Seventeen have more than 1,500 students, including five with more than 2,100. (Four schools on the neighbor islands that cover more grades than just high school are in the 600-900 range.)
Thomas Gans, an evaluation specialist for the Department of Education, said the principal advantage of smaller schools is the sense of community. "It's the notion that the school is a community in which every person has a place. In a large high school, only the very select get to participate in things such as athletics."
Many states, including Hawaii, are trying to break large campuses into smaller speciality programs, known as schools-within-in-a-school. When it comes to building new schools, it is cheaper and quicker to build one big school than two or three small ones in the same general area.
Star-Bulletin reporter Christine Donnelly and the Associated Press contributed to this report.