President Clinton claims to have the cure for what ails the U.S. education system: hiring 100,000 new teachers to reduce class sizes. There's just one problem (OK, two). First, there's no evidence that smaller class sizes alone lead to higher student achievement. And second, even if smaller classes were the ticket to better performance, 100,000 new teachers won't appreciably shrink the size of the average classroom.

The teachers unions and education gurus often point to Frederick Mosteller's research on the Tennessee STAR program as evidence that smaller class sizes boost academic achievement in early elementary school children. Recently though, Eric Hanushek, a researcher from the National Bureau of Economic Research, found flaws with the methodology of the Tennessee study, pointing out that the bulk of the data fail to provide systematic evidence of achievement gains.

Our own analysis of the 1998 National Assessment of Educational Progress data from the Department of Education backs this up. We found that after controlling for income, family background, and other demographic factors, fourth and eighth grade students in small classes (fewer than 20 students) do no better in reading achievement than those in large classes (more than 30 students).

Further, 100,000 new teachers will hardly make a dent in the nationwide student-teacher ratio. According to the Digest of Education Statistics, there are 46.8 million public school students and 2.8 million teachers, yielding a student-teacher ratio of 16.8-to-1. If 100,000 teachers were hired tomorrow, it would only drop the student-teacher ratio to 16.2-to-1. Even Mosteller's research finds positive effects from class-size reduction only after the class sizes have been reduced by at least a third.

If class-size reduction were a magic bullet, there wouldn't be an increasing number of success stories like New York City's Public School 161. When Irwin Kurz became P.S. 161's principal 13 years ago, the school's test scores ranked in the bottom 25th percentile in Brooklyn's 17th District. Today, P.S. 161 ranks as the best in the district and 40th out of 674 elementary schools in New York City, even though a majority of its students are poor. The pupil-to-teacher ratio at P.S. 161 is 35-to-1, but the teachers make neither class size, nor poverty, nor anything else an excuse for poor performance. According to Kurz, now the Brooklyn Regional Superintendent for Instruction, "Better to have one good teacher than two crummy teachers any day."

Instead of focusing on class-size reduction, the Clinton administration should be exploring ways to give principals like Kurz more freedom. Why not let individual schools spend federal education dollars any way they desire, so long as it leads to higher academic achievement? If some schools want to reduce class sizes, great. But it seems unwise to make class size a federal mandate, especially when figures from the administration's own Education Department don't support the benefits of smaller classes.

So far, the president is unmoved. His devotion to class-size reduction is such that he's already moistening his veto pen, this time over reauthorization of the Elementary and Secondary Education Act (ESEA). If Congress doesn't cave to his demands for 100,000 new teachers, he'll scratch the bill, regardless of the other good reforms - such as increased accountability - that it might contain. And with congressional budget leaders already cutting the president's $1.75 billion teacher-hiring proposal by a sizable amount, a veto appears certain.

Hiring more teachers might be good for teachers unions, which would love to see their membership rolls expand at taxpayer expense. But it will do little to help school children get a better education.

Nina Shokraii Rees is a former senior education policy analyst with The Heritage Foundation (www.heritage.org) and Kirk Johnson is a former policy analyst in Heritage's Center for Data Analysis.