As many as two-dozen Catholic schools may close in Brooklyn and Queens, and dozens more have been closing in other big cities. The Chicago Archdiocese announced the possible closing of 40 schools this year. For generations, Catholic and other parochial schools have well-served students of their own and other faiths. Catholic schools serve Catholic students as well as non-Catholic African-American families that sacrifice to meet tuition payments. They and taxpayers get a big bargain.

Harvard University political scientist Paul Peterson and I found that New York City Catholic schools produce substantially better learning, particularly for students in poverty, at less than half the cost of public schools. The availability of New York State examination results and school spending data enabled us to confirm previous investigations carried out in other cities. Catholic schools excel in achievement at substantially lower costs.

We compared the mathematics and reading achievement scores of all of the hundreds of Catholic and public schools in three New York City boroughs: Brooklyn, Manhattan, and the Bronx. Since public schools may more often serve special education students with visual, hearing, and real or imagined psychological problems, we omitted their scores so that only general education students in both types of schools were compared. Evaluations of special programs for children with presumed psychological handicaps often show they learn more in regular classes than being stigmatized and segregated in expensive special classes. In any case, we omitted their scores to avoid biasing the results.

In all grades available for analysis, Catholic schools in the three boroughs scored better on the state achievement tests than public schools. Even more illuminating was that Catholic schools succeeded much better than public schools in serving students in poverty. The differences between schools of middle-class and poor children were far smaller among Catholic schools than among public schools. Thus, Catholic schools not only achieved more but also more successfully solved the “poverty gap,” which is pervasive in American schools.

Our study in New York City is apparently the largest ever conducted and the first to study both achievement and spending. To make fair comparisons, we omitted the costs of special education from public school spending. We also excluded the costs of federal programs for children in poverty and bilingual programs because the public schools receive more funds for these programs.

Although these programs bring more money into public schools, evaluations often show no effects, and, in some cases, harmful effects. Bilingual education, for example, requires teaching children in their first language but denies them what they most need – practice in English. Similarly, independent evaluations of the federal program for children in poverty have generally shown no effects on reducing the “poverty gap” in achievement despite national spending of more than $125 billion since the inception of the program.

In addition, the New York City public schools have other large costs that we also omitted. These include the costs of transportation and food services and the huge administrative costs of the central office and community school boards.

With all these costs deducted, we found that the public schools spent on average about $5,250 per student. The Catholic costs averaged about $2,450, or 46.8% of the public school costs in the same neighborhoods.

How do Catholic schools do it? To find out, I visited Catholic and public schools in the boroughs. My classroom observations and principal interviews revealed that in public schools, programs and procedures were usually bureaucratically ordered by the central office, the community boards, and the U.S. Department of Education – entities that fund and regulate the public schools and their complicated programs.

The public schools rapidly replaced administrators and faced constantly changing mandates from above. Grade levels and attendance boundaries were altered without parental or staff consultation. In the public school classrooms, many students were inattentive, lacked books, and failed to complete assignments. They were often resting, chatting, and walking around and in and out of the classroom.

In contrast, Catholic schools had to compete for their “customers,” that is, parents and students. Perhaps as a consequence, interviews and observations in Catholic schools revealed an atmosphere of courtesy, fairness, and respect. The schools had strong principal leadership with a clear mission for learning, and most decisions were made at the school site.

An academic curriculum was taught well to large classes. Students kept notebooks of assignments and daily notes for each subject, and their homework was completed and graded every day. Parents and teachers were in close contact in the school and by telephone, which kept parents and teachers closely and frequently connected. Finally, the Catholic schools had few administrative and support staff, such as vice principals, program developers, consultants, and teacher aides.

I think the most essential feature of Catholic low-cost school success may not be Catholicism. Though often of the Catholic faith, few of today’s teachers in Catholic schools are members of religious orders. Rather, the key is that Catholic and other private schools that rely on tuition must compete for their customers, the parents. Treated badly, they walk. Treated well and given a serious academic program, parents, including those who must sacrifice greatly to pay tuition and who may not even be Catholic, retain their loyalty.

Given more than twice the money to spend per child, why can’t New York City public schools do nearly as well? Perhaps the time is finally ripe to let Catholic and other parochial and private independent schools compete on an even footing of public funds to better educate the city’s children and youth.

Mr. Walberg is Emeritus University Scholar and Professor of Education and Psychology at the University of Illinois at Chicago and Distinguished Visiting Fellow at the Stanford University Hoover Institution.