By now, everyone following the debate over charter schools in New York has been made aware of just how much money is flowing into these institutions. The conspiracy theories are rampant. WNYC radio ran a story called: “Who Is Behind the Pro-Charter Schools Group Fighting de Blasio?” “Wealthy, powerful people” was the answer. A recent New York Times headline summed up the conclusion of the critics: “Gilded Crusade for Charters Rolls Onward.”

Those who support Mayor DeBlasio’s attack on charter schools have speculated about the ulterior motives of people donating their own hard-earned money to support them. Diane Ravitch suggests that bankers and hedge fund managers are trying to “privatize” education while pretending that they are leading a new civil rights movement. A Daily News columnist speculated that they are funding charter schools so they can reap benefits from tax credits. The critics overlook a more likely motive: wealthy people donate to charters because those schools succeed in educating poor children.

One would think from this campaign that charter schools are controversial and are supported only by wealthy people, conservatives, or Republicans. Nothing could be further from the truth. President Obama has made charter schools a centerpiece of his program to raise educational standards across the country. Governor Cuomo has come out strongly in favor of charter schools. Public officials and educators across the political spectrum recognize the value of charter schools in promoting student achievement.

If we are going to have a debate about charter schools, it’s important to get the facts straight. First of all, charter schools are public schools, subject to public standards and funded by public money but supplemented by private donations to make up for the lower per pupil allocations charters receive from state and city governments. There are 183 charter schools now operating in New York City, serving 70,000 students, about 6% of the public school enrollment in New York City.

Charter Schools are independent of the district system, and thus have greater flexibility in the way they operate. They may develop their own academic curricula, choose staff, select teachers, and set academic goals. They can offer a longer school day or school year, which many do; and they can establish their own rules for student behavior and conduct. Most do not have unionized teaching staffs, which is a bone of contention among the teacher unions.

The students who benefit from charters tend to be poor and members of racial minorities. Among students enrolled in charter schools in NYC in 2011-12, 60% were African-American and 33% Latino. Almost three-quarters qualified for reduced price lunches and one in ten were in need of special education. Whatever the faults of charter schools, parents seem to like them–in 2013, there were 69,000 applicants for 18,600 available seats.

And why shouldn’t they? Students in charter schools perform as well or better than students in district schools. In 2011, 72% of 4th grade charter students performed at or above grade level compared to 62% of students in district schools; among 8th graders, the gap was wider, 69% to 52%. A report from Stanford University’s Center for Research on Education Outcomes found that attending a charter school in New York City had a large positive effect on math performance, and a mild positive effect on reading.

Eva Moskowitz’s 22 Success Academy Charter Schools have come in for heavy criticism from the Mayor and the teachers’ unions. Perhaps they are embarrassed at how well her schools perform compared to district schools. Success Academies rank among the top 1 % of all New York schools with 82 %t of fifth grade students passing the 2013 examinations. Fifth graders from Success Academy in Harlem ranked first in math achievement among 2,254 schools in the state.

So what are the keys to success? Contrary to popular belief, it’s not money. Charter schools still spend much less per pupil than traditional public schools. According to a report last fall from the Save Our States policy group, New York City charters in public school buildings spend $3,000 less per student than regular district schools. Teachers in charter schools are generally not union members, which partially accounts for the difference. In addition, charter schools do not have the enormous administrative overhead of district schools, which allows them to allocate manpower to the classroom.

The disconnect between per pupil spending and student performance should not be surprising to anyone who has looked closely at the issue. For the past 40 years, as government spending on education has skyrocketed, American student performance has remained stagnant, and in many ways has been in decline. Much of federal spending on public education simply rewards mediocrity by sustaining the status quo. Because unions generally reject any kind of pay for performance or try to minimize the role of student test scores in teacher evaluation, most districts simply pay teachers based on seniority.

By contrast, the money that flows into charter schools actually rewards student achievement. Charters that do not perform soon go out of business for lack of support or enrollments. Critics have targeted Ms. Moskowitz for the generous salary she receives ($487,00 in 2011 according to public reports). For what she and other charter leaders have achieved, they are undoubtedly being underpaid. Truth to tell, New York needs more “overpaid” educators like Ms. Moskowitz.

Let’s compare their salaries with those of public school executives. Randi Weingarten, head of the American Federation of Teachers, drew a salary in 2011 of close to $550,000; Michael Mulgrew of the United Federation of Teachers drew a salary if $295,000. In addition they are in line for generous pensions when they retire. Carmen Farina, new head of New York City’s public schools, receives an annual pension of close to $200,000 by virtue of her years of service as a teacher in the public school system, which (combined with her salary as Schools Chancellor) gives her a combined publicly paid income of $412,000 this year.

Yet Ms. Farina is responsible for a school district with an overall graduation rate of about 60%. That means 4 in 10 students sent off to their first day of 9th grade will not graduate in four years. Even worse, among students who do graduate, just 22% were college and career ready, according to the state’s standards.

The issue should not be how much Ms. Moskowitz and other charter school leaders are paid or why private donors support charter schools (the answer is obvious) but why taxpayers are getting so little for the money invested in conventional public schools. The misguided campaign against charter schools is a diversion from the problems that beset public education. If charter schools are guilty of anything, it is in showing how much can be accomplished when schools are set up with student achievement as the number one priority.

Mr. Piereson is a senior fellow at The Manhattan Institute.