President Clinton sent every principal in the country a book promoting it. The initiative must have failed, because today you don't see many kids in school uniforms and the issue seems to have dropped from the media radar screen.
It is the nature of much so-called educational innovation to capture the imagination with or without adequate evidence to support claims. People can intuitively agree that having same sex classes might help some kids, but when you look at what studies exist to support this, there isn't much.
Title IX of the Educational Amendments of 1972 is the landmark legislation that bans sex discrimination in schools, whether it is in academics or athletics. It states:
"No person in the U.S. shall, on the basis of sex be excluded from participation in, or denied the benefits of, or be subjected to discrimination under any educational program or activity receiving federal aid."
This latest initiative appears to have started when the US Department of Education announced that Title IX restrictions would not apply to experiments in grouping students on the basis of sex. I can find no reason why federal law is being waived for this except that many feel that Title IX, the gender equity law, applies only to how much money schools should be spending on school sports.