MIAMI – In a distressed neighborhood north of Miami’s gleaming downtown, a group of enthusiastic but inexperienced instructors from Teach for America is trying to make progress where more veteran teachers have had difficulty: raising students’ reading and math scores.

“These are the lowest performing schools, so we need the strongest performing teachers,” said Julian Davenport, an assistant principal at Holmes Elementary, where three-fifths of the staff this year are Teach for America corps members or graduates of the program.

By 2015, with the help of a $50 million federal grant, program recruits could make up one-quarter of all new teachers in 60 of the nation’s highest need school districts. The program also is expanding internationally.

That growth comes as many districts try to make teachers more effective. But Teach for America has had mixed results.

Its teachers perform about as well as other novice instructors, who tend to be less successful than their more experienced colleagues. Even when they do slightly better, there’s a serious offset: The majority are out of the teaching profession within five years.

“I think, ultimately, the jury is out,” said Tony Wagner, a professor at the Harvard Graduate School of Education, and an instructor to the first class of TFA corps members.

Teach for America teachers not only work with the poor, but also English language learners and special education students. They provide an important pipeline of new teachers. But critics cite the teachers’ high turnover rate, limited training and inexperience and say they are perpetuating the same inequalities that Teach for America has set to eradicate.

“There’s no question that they’ve brought a huge number of really talented people in to the education profession,” said Kati Haycock, a longtime supporter of TFA and president of The Education Trust, which advocates on behalf of low-income and minority children.

But, she said, “Nobody should teach in a high poverty school without having already demonstrated that they are a fabulous teacher. For poor kids, education has to work every single year.”

Wendy Kopp started Teach for America while studying public policy at Princeton. For her senior thesis, she developed a plan to place top college graduates in the poorest schools. She sent the plan to dozens of Fortune 500 executives. Within a year, she had raised $2.5 million and had 2,500 applications.

Over the past 20 years, thousands of recent college graduates have taught for two years in some of the most challenging classrooms in hopes of helping close the achievement gap. Applications have doubled since 2008. Foundations have donated tens of millions.

With Teach for America’s guidance, groups are being established in India, Chile and other places with deep educational inequalities.