Donald Cohen, executive director of “In the Public Interest,” an organization that fights privatization of public services, writes about the curious combination of people who poured serious money into the Massachusetts charter school battle last fall.

When the Massachusetts Office of Campaign and Political Finance forced a pro-charter school political organization to reveal its donors, guess which words jumped off the page? Bain Capital.

Of the more than $15 million Families for Excellent Schools spent pushing last November’s controversial ballot initiative to increase the number of charter schools in Massachusetts, $1.4 million came from Bain investors, including Romney’s fellow cofounder Josh Bekenstein.

The initiative was voted down—parents, teachers, and residents mobilized to protect traditional public schools—but until now we had little proof that a shadowy gang of private investors and billionaires were leading the charge.

Donors included the owner of the Oakland Athletics baseball team, the billionaire hedge fund manager Seth Klarman, Alice Walton of the Walmart family fame, and even Massachusetts’s current chairman of Massachusetts Board of Elementary and Secondary Education, the venture capitalist Paul Sagan.

So why does Bain and a handful of billionaires want more charter schools?

We really don’t know, at least yet. Like everything in finance, the tangled knots and paper trails are seemingly endless.

Maybe they’re just being nice and philanthropic, trying to help, as Romney himself once called them, “inner city kids.” But maybe they’re up to something else.

In our report on California’s charter schools, we dug into the $2.5 billion in taxpayer dollars and subsidies spent in the past 15 years to help private groups lease, build, or buy school buildings. Due to a severe lack of regulation, some of this money has ended up in the pockets of investors and executives.

For example, two schools in Stockton, California, are renting space for three and half times the market rate from a company with business ties to the CEO of the charter operator that oversees them.

Los Angeles’s Alliance network of charter schools has received more than $110 million in federal and state taxpayer support for its facilities, which are not owned by the public, but are part of a growing empire of privately owned real estate now worth in excess of $200 million.

The bottom line is, there’s lots of taxpayer money sloshing around in an unregulated market, and few people know where it’s going.

For some well-meaning educators and parents, charter schools are about innovation and alternative learning. But for the investors and billionaires behind the growing charter school industry, they seem to be about something else altogether: private control of taxpayer money.