FROM our apartment you can see the front door of our children’s public school. It’s a bright red double door made of solid wood and framed in brown-red brick. Last summer I spent a lot of time looking at that door with anticipation and excitement. We had just moved to the Upper East Side of Manhattan from California, and had chosen the neighborhood for its school.

On the second Sunday after classes started, happy and hectic, I glanced out the window and saw a large group of people gathered in front of the schoolhouse door. They had a table, brochures, a tray of lollipops and a four-foot-tall sign. It turned out that they were part of an evangelical ministry and that our school was their church.

I decided to attend the service.

“Notice the names of the children on pieces of paper,” the pastor advised his flock. I looked around and saw the posters the kids had made, with their charming snapshots from summer holidays and rambling lists of likes and dislikes. “Pray for them!” the pastor continued. “Pray that the families of this school will come to know Jesus and say, ‘This is a House of God!’ ”

The pastor’s daughter, a lively 8-year-old who attends a private Christian school, took me on a brief tour through parts of the school I had not yet seen. “This is my dad’s church!” she enthused.

After the service, I chatted with the pastor and asked how much it cost to rent the school. “Oh no,” he said. “We don’t pay rent! New York is way too expensive! We just pay the custodians’ fee.” I learned that the church was using the school not just on Sunday mornings and evenings, but also on some Wednesday and Friday nights, and that it paid a pittance for the privilege — far less than the nearly $100,000 that the P.T.A. spent last year to renovate the restrooms the church members were using.

Ours is just one of at least 60 New York City schools that have doubled as rent-free houses of worship — the vast majority of them evangelical Christian churches — in their off-hours. Many have little connection with the school communities. It’s hard to imagine, for example, that the Village Church at Public School 3 in the West Village — a church that runs a Gender Affirming Ministry Endeavor associated with the movement to “cure” gay men and lesbians — is representative of the neighborhood.

A number of the new churches are the work of national “church-planting” organizations attracted to New York by the combination of cheap space and the opportunity to save the city from its apparent godlessness. Some are closely associated with national groups known for their hostility to “government education.” The church that meets at my daughter’s school is associated with a movement that instructs its members to pray for a Christian “reformation” of American education and for the election of like-minded political leaders.

In some communities, parents and school administrators have complained that representatives of the churches have made use of their proximity to students to approach children for religious purposes. A friend in TriBeCa told me he was taken aback when his daughter asked him, “Daddy, is the church part of our school?”

The situation originated in a 2001 decision, Good News Club vs. Milford Central School, in which the United States Supreme Court appeared to suggest that keeping religious groups out of schools after hours amounted to discrimination against their religious views.

Subsequent federal rulings effectively forced the city to open school doors to nearly any religious group that asked for the privilege. But since school facilities are often available only on Sundays (when sports teams and extracurricular clubs are less likely to need space), Jews and Muslims, for example, were mostly shut out.

On June 2, the United States Court of Appeals for the Second Circuit ruled that the city could restrict religious congregations from conducting worship services in schools. To exclude an activity from a school because it is religious in nature, Judge Pierre N. Leval wrote, is not to discriminate against it on account of its religious viewpoint. Indeed, the school system does not give access to partisan groups, and no one supposes that they are losing their freedom of speech just because they can’t get free space. Using the school system to subsidize houses of worship, on the other hand, risks violating the Constitutional ban on the establishment of religion.

In light of this ruling, the city should enforce its original policy and exclude the use of school facilities for worship services. A near-term problem — and an example of precisely why this kind of entanglement should be avoided in the first place — is that many churches have come to depend on the schools for their survival. The city should seek a way to gradually end these relationships.

I could go on about why my daughter’s photo should not be made available for acts of worship, or why my P.T.A. donations should not be used to supply furniture for a religious group that thinks I am bound for hell, or why in a city blessed with an uncountable number of faiths it’s foolish to get schools tangled up in religion. But maybe it’s just that I imagine that that big red door is about education for all, not salvation for a few. Sometimes a building is more than a building.