IF YOU have a drafty home, you know it's smarter and cheaper to fix the broken window than to turn up the thermostat to stay warm.

That's just common sense, and it's the same approach I've taken to fixing Pennsylvania's broken system for funding charter and cyber-charter schools, whose cost has risen at an unsustainable rate over the last four years, to nearly $1 billion a year.

Pennsylvanians are mired in the worst economic calamity since the Great Depression. They simply can't afford to keep throwing good money at an idea that, no matter how well-intentioned or how successful, is so financially inefficient.

As the commonwealth's independent fiscal watchdog, I've urged the governor to impose a moratorium on the opening of new charter schools until the problem is fixed - because the solution to heating a home with a broken window isn't to open more windows and hope for a different result.

Charters are independent nonsectarian, nonprofit public schools established through a charter granted by a public school board. (The charters of cyber-charter schools, which educate via the Internet, are granted by the state Education Department.)

Enrollment in charters has skyrocketed over the last decade or so, to more than 73,000 students. But because of the flawed funding formula, the cost has risen even faster.

The most wasteful component is the premium the state pays to public schools that lose students to charters. That reimbursement jumped 87 percent from the 2004-05 to the 2008-09 school years, from an average of $1,673 per student to $3,122, according to a report issued by the Department of the Auditor General. (It's available at www.auditorgen.state.pa.us.)

Think about it. About $228 million, more a fourth of the nearly $1 billion that Pennsylvania taxpayers spent on charter schools in 2008-09, didn't go to educating children. Instead, it was a premium payment the state made to school districts for no longer having to educate those students.

You don't need a Ph.D. to understand that this is not a good deal for taxpayers. Sadly, however, it's not the only flaw in the funding formula.

Another inequity to taxpayers is the wide divergence that school districts pay to charter schools for educating a child. For example, the Greater Nanticoke Area School District in Luzerne County paid a tuition rate of $6,035, compared with $15,174 paid by the Jenkintown School District in Montgomery County for students attending the same cyber-charter school. The net result is that Jenkintown taxpayers may, in effect, be subsidizing tuition for cyber-charter students from less financially wealthy public school districts.

My call for a moratorium on charter expansion until all of this is fixed is not anti-charter or anti-parent. I have been an ardent supporter of alternative forms of public education. I was one of only two Democrats who voted for the charter school law in 1997 when I was a member of the state Senate because I firmly believe that a good education is fundamental to professional success.

A moratorium on new charters wouldn't deny any family the right to enroll their child in a charter - it would simply force them to enroll that child in one of the 135 charter schools already in existence.

A moratorium until the funding is fixed isn't punitive, but a commonsense move to strike a balance between the needs of families and the cost to taxpayers. The system is far out of balance, hurting taxpayers.

The longer the state uses the flawed formula, the more unsustainable it becomes to fund charters. And with the tough economy, the current inefficiencies in the charter funding formula put the long-term opportunity for growth of charters in Pennsylvania in jeopardy.

THAT'S WHY I hope that the Gov. Rendell and the General Assembly, or next governor, will take swift action to fix the flawed charter funding formula. Taxpayers can't afford the premium payment for students attending charter schools.

Jack Wagner is Pennsylvania's auditor general, the independent fiscal watchdog of taxpayer money.