TEACH FOR AMERICA (TFA), a not-for-profit organisation founded in 1990, places its young “corps members” at schools in poor areas to teach for two years. Most come fresh from college, and they learn mainly on the job. On September 10th a report for the Institute of Education Sciences (IES), the research arm of America's education department, suggested that TFA’s members excel at teaching maths (although older studies suggest they do no better than ordinary teachers at instructing children how to read). The report, which examined TFA members teaching maths in middle and high schools, found that the improved test scores of pupils were equivalent, on average, to an extra 2.6 months of school. Despite this seeming proof of TFA’s impact in classrooms, and its larger social mission, the organisation has many critics. Why?

The IES study’s methodology means its findings cannot be taken as representative of the not-for-profit’s work in general. Firstly, it looked at TFA members teaching secondary maths, when actually most of the organisation’s members work in primary schools. For example, in the Houston school district, with roughly 10,000 teachers, there were only 13 TFA high school teachers in 2010. Secondly, although TFA recruits were better in maths classrooms than other teachers, they were also more likely to be white, male and to have attended “more selective” colleges than those teachers with whom they were compared. That said, TFA is actually more diverse than the study suggests: 39% of its latest recruits come from minority backgrounds.

TFA’s approach to teacher preparation, and provision of only five weeks' training before placing recruits in front of students, attracts criticism from those who think the recruits aren’t ready for the challenges that await them. Ryan Vernoush, a member of Minnesota’s Board of Teaching and a former teacher of the year in the state, believes placing inexperienced young people in front of “marginalised students” only serves “to perpetuate the status quo of inequity”. Denise Specht, president of Education Minnesota, the state’s largest teaching union, says that career teachers “value experience” whereas TFA “equates enthusiasm with experience”. Her members have to compete for with TFA recruits for teaching posts, despite having lengthier training. In the eyes of the union that means that the TFA undermines professional teaching qualifications. Another interpretation of the fuss is that bright young graduates are taking the jobs of career teachers (and sometimes showing them up).

Two-thirds of TFA’s 32,000 alumni have remained in the field of education. Despite controversies, the organisation is an increasingly significant voice in debates about school reform and privatisation, partly as a result of the lofty positions many of its former members now hold. One, Cami Anderson, is the superintendent for Newark’s schools; another, Mike Johnston, is a state senator in Colorado. Some celebrities and philanthropists are also behind it: John Legend, a popular singer, serves on TFA’s national board and the Walton Foundation, funded by members of the family behind Walmart, has given it more than $100m. TFA’s approach to teacher training is likely to influence educational policy in America as the number of its influencial alumni grows.