The 2008 TIME 100

It's hard to know exactly what Wendy Kopp was expecting back in 1989 when she came up with a big idea for her senior year thesis at Princeton University. It's safe to assume, however, that she didn't expect her professor to call her "quite evidently deranged," which he did. Kopp, to her credit, chose not to listen. That turned out to be a very good thing for millions of kids.

The wild idea Kopp, now 40, had was to launch a U.S. national teaching corps, similar to President John F. Kennedy's Peace Corps, that would recruit young teachers straight out of college and sign them up for a two-year hitch working in some of the country's more disadvantaged schools. Since income too often determines where you live, and where you live too often determines whether you'll go to a failing school or a good school, Kopp saw more than a simple problem of educational inequity at work. She saw what she considered the most important civil rights issue of her generation.

In 1990, Kopp, then 23, raised $2.5 million to get her teaching corps started. From that beginning came Teach for America, a nationwide organization that today boasts more than 5,000 member teachers, who work in communities all over the country and reach 440,000 kids. Some 12,000 veterans of Teach for America have continued their teaching careers, often providing leadership for troubled schools in their own communities. A 2005 study showed that 75% of school principals consider Teach for America teachers more effective than other teachers, and a 2004 study showed Teach for America students do better than other kids in math. Deranged or not, Kopp's idea is working—and as a result, more kids are learning.