Each year, thousands of New York City parents pray that their children get offered a seat in a charter school, and a new study confirms that they have good reason to do so—the children will do much, much better. New York State should make this life-changing alternative available to any family who wants it.

Charter schools are public schools that operate largely independently, functioning in essence as their own school districts. Without the restrictions imposed by collective- bargaining agreements with teachers, charter schools are free to experiment in ways that traditional public schools cannot. Thus, the type of education charters provide varies substantially—and not only from that offered in the traditional public sector, but also among charters themselves.

Charters receive taxpayer dollars on a per-pupil basis, but unlike traditional public schools, which are assigned students based on residential zones, charter schools get their students through applications. Thus, for a charter school to remain open, it must attract enough students to pay its bills. New York’s Charter Schools Act of 1998, passed under Republican Governor George Pataki, capped the number of the state’s charter schools at 100. Due to high demand, however, the state quickly exceeded this limit, and Democratic Governor Eliot Spitzer raised it to 200. The state will soon bump up against that ceiling as well.

New York Mayor Michael Bloomberg has made charter expansion part of his education reform agenda. When he took office in 2002, there were just 17 charter schools in New York City. Now there are close to 100, serving 30,000 students, with another 40,000 on waiting lists.

But high demand doesn’t necessarily mean high quality. That’s why a new study released this week by Stanford economist Caroline Hoxby is so important. It leaves little doubt that students benefit when they attend a New York City charter school. Hoxby’s study follows a design similar to that of a medical trial—a procedure considered the “gold standard” of social science research. She compares the academic performance of two groups of randomly selected students: those who had applied to and enrolled in a charter school and those who had applied but wound up on a waiting list. Hoxby’s method thus avoids self-selection bias, since both groups applied to a charter school.

Her findings are striking. Students in Gotham charter schools make significant improvements in both math and reading compared with where they would be had they remained in their previous public school. Hoxby estimates, in fact, that if Harlem students attended a charter school from grades kindergarten through eight, they would close about 86 percent of the vast test-score deficit that exists between them and students in Scarsdale.

And New York City’s charter schools are not only more effective than traditional public schools, but less costly, too. This year, the city’s charter schools will receive $12,205 per pupil in state funding. That’s a lot of money, but it’s only 70 percent of what a traditional public school receives per pupil. Some charter schools supplement these state dollars with private donations, but the vast majority doesn’t make up the difference in funding.

The bottom line? It’s time for the state to remove the cap on the number of charter schools so that more children have an opportunity for a better life.

Marcus A. Winters is a senior fellow at the Manhattan Institute.