ProPublica's investigation of the funding and mission of Teach for America discovered that TFA is an arm of the charter movement, which aims to replace public schools with non-union private charter school. Documents obtained by ProPublica show that the Walton foundation, a staunch supporter of school choice and Teach For America’s largest private funder, was paying $4,000 for every teacher placed in a traditional public school — and $6,000 for every one placed in a charter school. Diane Ravitch says: "This is an eye-popping article, an exemplar of investigative reporting. It begins: "When the Walton Family Foundation announced in 2013 that it was donating $20 million to Teach For America to recruit and train nearly 4,000 teachers for low-income schools, its press release did not reveal the unusual terms for the grant."