Charter schools in the United States, which offer alternative education with the public funding they receive, are being scrutinized by several nongovernmental organizations in order to investigate the financial transparency of the schools.

The Gülen Movement, which operates a vast network of schools on six continents, allegedly operates a large number of charter schools in the U.S. Many schools disavow any links to the movement, however, especially after a terror probe was launched in Turkey against Gülenists.

A report by the Center for Democracy and Media found that more than $3.7 billion was allocated to charter schools by the U.S. federal government, but the public is not informed about how many schools received such funds or the amount. The report said there is "an epidemic of fraud, waste and mismanagement" in charter schools, which are "often policed by proponents of the charter system." The report also claimed to discover "ghost schools," schools that do not exist even though federal grants were allocated to those schools. Center for Democracy and Media Executive Director Lisa Graves said in a statement published on the organization's website that taxpayers know far too little about how much their federal tax dollars are being used to fund charter schools, and there was little information provided by states about how tax money is being spent by such schools or the for-profit firms to which they are linked.

The report comes at a time of an investigation by the FBI into Concept Schools, a chain of charter schools founded in 2002 accused of links to the movement, although its administrators, all Turkish nationals, deny any such links. The investigation is looking into allegations that the charter school chain diverted state funds it acquired to individuals and institutions tied to the Gülen Movement.

According to its website, it operates 17 schools in Ohio, four in Illinois, three in Missouri, three in Indiana and one each in Minnesota, Michigan and Wisconsin. Overall, there are more than 140 schools in 26 states operated by groups linked to the Gülen Movement.

The investigation began after a series of raids in June 2014 on schools and offices of the Concept Schools' network in Illinois, Ohio and Indiana. The FBI seized documents regarding the schools' contracts, documents related to e-rate grants and documents related to money transfers. E-rate is a program by the Federal Communications Commission (FCC) that provides discounts to schools in the U.S. to acquire affordable equipment for telecommunications and Internet access. Concept Schools Vice President Salim Uçan denied the charges and told Daily Sabah they renewed their grants despite the ongoing FBI inquiry.

Harmony Public Schools, which operates 46 schools in Texas, had also faced accusations by a nongovernmental organization opposed to charter schools, ranging from tampering with tests to hiring unqualified teachers.