The Walton Family Foundation is pumping $6 million into a Washington-based group that promotes private school vouchers in D.C. and around the country — a donation that it hopes will double the number of students using tax dollars to pay private school tuition.

The foundation, created by the heirs of Wal-Mart founder Sam Walton, is giving the money to the Alliance for School Choice, a nonprofit that has been promoting and lobbying for school voucher programs in D.C., Ohio, Indiana, Arizona, Georgia, North Carolina, Florida, Wisconsin, Pennsylvania and elsewhere.

Proponents of vouchers say they give low-income children the opportunity to escape troubled public schools. Critics say that tax dollars are better spent improving public schools.

The $6 million infusion will basically double the budget of the Alliance for School Choice, which reported total revenue of $6,380,488 in 2011, according to federal tax filings. The chairwoman of the organization is Betsy DeVos, a high-profile Michigan Republican leader who is married to Dick DeVos, heir to the Amway fortune.

The alliance shares staff, facilities and other resources with the American Federation for Children, a nonprofit also founded by Betsy DeVos and its political arm, the American Federation for Children Action Fund.

Together, these three organizations have lobbied state legislatures to create programs that allow low- and middle-income students to use public tax dollars to attend private schools, including parochial schools. The groups have also helped create donation tax credits, which are state tax credits given to individuals or businesses who donate to private school scholarships.

Vouchers were once thought to be moribund, but came roaring to life in 2010 in states where Republicans took control.

Kevin P. Chavous, a former D.C. Council member who is executive counsel to the American Federation for Children, said the grant will allow his group to “aggressively” market school vouchers to low-income families.

“I’m amazed in Southeast and Northeast D.C. at how many people, particularly low-income parents, don’t know about this option,” Chavous said. “When they find out about it, they love it. We see this around the country, whenever these choice programs come into existence. We assume that once it’s in place, we assume that people know about it, and they don’t.”

Currently, about 300,000 K-12 students around the country are paying for private schools with public tax dollars, according to the Alliance for School Choice. The group says it wants to double that number.

The alliance plans to use some of the Walton funding to help communities implement their voucher programs.

The D.C. voucher program is the only federally funded type in the country. The federal government has poured $152 million into the D.C. Opportunity Scholarships Program since it was created by Congress in 2004. About 5,000 students have received vouchers to attend private schools in the District.

The execution of the D.C. voucher program has been rocky, with inadequate safeguards over the millions of dollars in federal funds, insufficient information for parents and a student database that is riddled with incomplete information, the Government Accountability Office found in a report released last month.

The GAO found the trust’s policies and procedures “lack detail in several areas related to school compliance and financial accounting, which may result in little overall accountability for program funds.”

Those conclusions echo a Washington Post investigation published last November, which found that the 52 D.C. private schools approved to participate in the voucher program are subject to few quality controls and offer widely disparate academic experiences.

The Post found that hundreds of students use their voucher dollars to attend schools that are unaccredited or are in unconventional settings, such as a family-run K-12 school operating out of a storefront, a Nation of Islam school based in a converted Deanwood residence and a school built around the philosophy of a Bulgarian psychotherapist.

At a time public schools face increasing demands for accountability and transparency, the voucher schools operate in relative isolation. The government has no say over curriculum, quality or management.

Of the District students now receiving vouchers, more than half attend Catholic schools and a handful are enrolled at prestigious independent schools such as Sidwell Friends, where President Obama sends his daughters.

The most comprehensive study of the D.C. program, released by the U.S. Department of Education in 2010, found that voucher students were more likely to graduate than peers without vouchers, based on data collected from families. And parents reported that their children were safer attending the private schools, though the students themselves perceived no difference.

But the study found “no conclusive evidence” that the vouchers improved math and reading test scores for those students who left their public schools.