The nation's best-known researcher on homework has taken a new look at the subject, and here is what Duke University professor Harris Cooper has to say:

Elementary school students get no academic benefit from homework -- except reading and some basic skills practice -- and yet schools require more than ever.

High school students studying until dawn probably are wasting their time because there is no academic benefit after two hours a night; for middle-schoolers, 1 1/2 hours.

And what's perhaps more important, he said, is that most teachers get little or no training on how to create homework assignments that advance learning.

The controversy over homework that has raged for more than a century in U.S. education is reheating with new research by educators and authors about homework's purpose and design.

No one has gone as far as the American Child Health Association did in the 1930s, when it pinned homework and child labor as leading killers of children who contracted tuberculosis and heart disease. But the arguments seem to get louder with each new school year: There is too much homework or too little; assignments are too boring or overreaching; parents are too involved or negligent.

"What should homework be?" asked veteran educator Dorothy Rich, founder of the nonprofit Home and School Institute. "In the biggest parameter, it ought to help kids make better sense of the world. Too often, it just doesn't."

In the nation's classrooms, teachers say they work hard to conform to school board policies and parent demands that do not always match what they think is the best thing for children.

Yet teachers themselves don't uniformly agree on something as basic as the purpose of homework (reviewing vs. learning new concepts), much less design or amount or even whether it should be graded. And the result can be inconsistency in assignments and confusion for students.

That is part of the reason some educators and authors are making new cases for the elimination of homework entirely, including in the new book "The Homework Myth," by Alfie Kohn.

Kohn points to family conflict, stress and Cooper's research as reasons for giving kids other things to do to develop their minds and bodies after school besides homework.

"I am always fascinated when research says one thing and we are all rushing in the other direction," Kohn said.

"It is striking that we have no evidence that there is any academic benefit in elementary school homework," he said. "Then people fall back on the self-discipline argument and how it helps students learn study skills. But that is an urban myth, except that people apply it in the suburbs, too."

In 1989, Cooper, now a professor of psychology and director of Duke's Program in Education, published an analysis of dozens of studies on the link between homework and academic achievement.

His conclusions: The research base showed no correlation between academic achievement and homework -- besides reading -- in elementary school, a small benefit in middle school and more for high school.

This spring, he co-authored another paper in the Review of Educational Research after reviewing various newer studies done on homework from 1987 to 2003, and he offered a few additions to his conclusions.

This time, he said, there was some evidence that, in grades 2 through 5, students do better on unit tests when they do short homework assignments on basic skills that relate directly to the test.

And, he said, it appears that more than two hours of high school homework, and more than 1 1/2 hours of middle school homework, have no academic benefit and may produce negative results.

Other educators, such as Linda Darling-Hammond, a Stanford University education professor and researcher, say that many of the studies Cooper evaluated were not tightly controlled and not authoritative but that his conclusions make sense.

Darling-Hammond said Cooper also is correct in pointing out that many teachers lack the skills to design homework assignments that help kids learn and don't turn them off to learning.

Today, schools of education provide varying levels of training in the art of designing homework assignments that are more than busywork, usually imbedded in courses about curriculum. Many, however, offer none, and teachers say they wish the schools had.

"One isn't born knowing how to make sensible lesson plans and homework assignments," said Karen Zabrowski, a seventh-grade reading teacher at Chippewa Falls Middle School in Wisconsin.

But teacher knowledge is often trumped by school system policies, created by school boards whose members are often not educators, teachers have said.

Timothy Naughton said he learned about homework at Fordham University in the 1990s. "We agreed it wasn't the best practice for younger students, but we knew everybody was going to make us give it anyway, so we talked about how to reconcile the two positions," said Naughton, who has taught in various elementary grades and is a kindergarten teacher in East Stroudsburg, Pa. He gives no homework but suggests that parents read and practice basic skills with their kids.

Kohn said that if he were education czar, kids would not be assigned homework but would wind up learning anyway. That's what happened at the private Kino School in Tucson, where traditional homework was banned but kids designed their own after-school projects because they wanted to keep learning.

Cooper said that eliminating homework makes no more sense than "piling it on" and that the answer is somewhere in between.

Georgia Leigh, 16, an 11th-grader at Bethesda-Chevy Chase High School, tends to support the middle ground. It was not until 10th grade, she said, that homework was more than busywork. What changed then, she said, was that she began to be assigned more reading.

"I feel like I'm learning more when I'm reading than when I'm filling out math sheets," she said. "If homework were eliminated? I'd read anyway."