This is the VOA Special English Education Report.

In nineteen ninety-nine, twelve percent of public elementary schools in the United States required students to wear uniforms. Just three years later, estimates were almost double that.

Students leave a Cleveland, Ohio, high school in January 2006. A study of six big-city Ohio public schools showed students who were required to wear uniforms had improved graduation, behavior and attendance rates. Academic performance was unchanged.

Some middle and high schools have also joined the movement. Yet studies find mixed results from requiring uniforms. And some schools have turned away from such policies.

Supporters believe dressing the same creates a better learning environment and safer schools. The school district in Long Beach, California, was the first in the country to require uniforms in all elementary and middle schools.

That was in nineteen ninety-four. The example helped build national interest in uniforms as a way to deal with school violence and improve learning.

Findings in Long Beach suggested that the policy resulted in fewer behavior problems and better attendance. But researcher Viktoria Stamison has looked at those findings. She says they were based only on opinions about the effects of uniforms.

She says other steps taken at the same time to improve schools in Long Beach and statewide could have influenced the findings. The district increased punishments for misbehavior. And California passed a law to reduce class sizes.

Her report is among several in a book published last year called "Uniforms in Public Schools: A Decade of Research and Debate."

In Florida, for example, researcher Sharon Pate found that uniforms seemed to improve behavior and reduce violence. In Texas, Eloise Hughes found fewer discipline problems among students required to wear uniforms, but no effect on attendance.

Sociologist David Brunsma has studied school uniform policies since nineteen ninety-eight. He collected the reports in the book. In his own study, he found that reading and mathematics performance dropped after a school in rural Pennsylvania required uniforms.

Political and community pressures may persuade schools to go to uniforms to improve learning. But David Brunsma and others believe there is not enough evidence of a direct relationship. In fact, he says requiring uniforms may even increase discipline problems.

But researchers also say studies of uniform policies are often scientifically limited. They say more work is needed to get better information.

And that's the VOA Special English Education Report, written by Nancy Steinbach. For more on this debate, go to voaspecialenglish.com. I'm Steve Ember.