Hope was scarce for Joel Camas, 16, last winter. His mother had spent $11,000 on lawyers — nearly all of her money — but mother and son remained on a trajectory toward deportation back to Ecuador, and Joel’s life in New York City seemed to be unraveling.

In the Bronx, his high school was a lifeline. Against a drumbeat of immigration arrests, teachers offered comfort and helped him plan for the future he dreamed of as an auto mechanic or Army soldier. In his spare time, he liked hanging out with classmates to play soccer and eat pepperoni pizza.

And, crucially, school staff members and friends worked with a pro bono lawyer to try to persuade immigration officials to let Joel, who is undocumented, stay in America.

As President Trump’s immigration crackdown has begun to target more underage migrants, New York schools have become a quiet locus of resistance, with teachers, classmates and neighbors banding together in their defense. At least five migrant students have been detained or deported since January in New York City.

In interviews, more than a dozen people connected to school-age migrants said they were dismayed by what they described as the federal government’s intimidation of children. They have built an informal network of allies and shelters to cocoon the city’s students, in some cases offering lodging or escorting them to and from school so that their parents avoid interactions with law enforcement. There have been no reported cases of federal agents detaining children at school in New York or elsewhere.

Because their efforts risk drawing the attention of administration officials who have sometimes exacted retribution against those who impede their clampdown, many advocates and educators have acted in secret.

“That’s what New Yorkers are best at: being able to come together in a crisis,” said Norma Vega, the principal of Ellis Preparatory Academy, whose student Dylan Lopez Contreras was detained by immigration officials earlier this year. She added: “There’s a lot more good than there is bad.”

Mr. Lopez Contreras, 20, was the first public school student in the city to be arrested during Mr. Trump’s second term. Ms. Vega said that the city’s outpouring of support for him and other young migrants reminded her of the kindness that strangers extended to her mother after she survived the Sept. 11, 2001, terrorist attacks.

In the case of another student — Mamadou Mouctar Diallo, 20, who attended Brooklyn Frontiers High School — teachers rallied on the steps of the city Department of Education’s headquarters after he was detained in August by Immigration and Customs Enforcement agents during a routine court appearance at 26 Federal Plaza in Lower Manhattan. That building, and the immigration courtrooms inside, have become the epicenter of detentions in New York City.

Mr. Diallo, 20, is an asylum seeker from Guinea who entered the country last year. He remains in confinement in Lords Valley, Pa.

Tricia McLaughlin, a spokeswoman for the Department of Homeland Security, said in an email that ICE does not target schools or children.

“The media is sadly attempting to create a climate of fear and smear law enforcement,” Ms. McLaughlin said. She added: “ICE is not conducting enforcement operations at, or ‘raiding,’ schools.”

Sometimes, help comes from beyond the walls of the classroom.

On a blistering June afternoon before classes broke for the summer, an alliance of a half-dozen panicked neighbors gathered a few blocks from P.S. 015 in the Brooklyn neighborhood of Red Hook. Someone at the elementary school had called a mother who lived nearby amid whispers that ICE agents were waiting for her outside the campus. The neighbors debated what to do.

What if ICE agents were also lurking near the family’s home? Should someone stay with the mother? Was the Police Department in on it?

A few minutes later, they instructed the woman to barricade herself inside, and together they marched to the school and delivered the child home. ICE never showed up.

Elsewhere in New York this year, a principal and a teacher’s mother attended two students’ deportation hearings. Upstate, a teacher gave refuge to a family that was too afraid to go home after being detained and released by immigration officials.

With the backing of the teacher’s union in New York City, the United Federation of Teachers, schools have trained educators and parents to distribute red cards — documents that assert people’s constitutional rights, regardless of immigration status.

Educators have also helped students understand how to avoid interactions with immigration officials as part of a broader plan to help families seeking asylum in the United States. A New York City public school program devotes resources for migrant students, including transportation to school and English-language lessons.

The New York City schools chancellor, Melissa Aviles-Ramos, has denounced the detention of students, vowing to keep them safe and to defend their rights. Educators have expressed concern that many undocumented kids are not showing up to school because of increased immigration enforcement.

“Public schools are the bedrock of democracy, so I’m glad to see certain public schools standing up,” Sari Beth Rosenberg, a teacher at a New York City public high school and a co-founder of the nonprofit Teachers Unify to End Gun Violence, said. “I think if we can use the public schools to educate and empower young people, I hope they can come home and educate their family members who are very frightened right now.”

Schools that are bracing for potential activity have been offered support by the staff of City Councilman Lincoln Restler and State Senator Andrew Gounardes, both Democrats who represent districts where residents have gathered to help undocumented students. Many schools have developed guidelines for children and parents during pick-up and drop-off, as well as for principals to share news about ICE sightings.

Between classes, school-age migrants swap information among one another about community organizations that can help tether them to New York.

Joel, the teenager from the Bronx, met his attorney, Beth Baltimore, through a youth social services center called the Door, which offers 12- to 24-year-olds essential services such as health care, mental counseling and legal assistance.

“Someone will become a member of the Door, and suddenly, the next week, all of their friends become members of the Door, too,” Ms. Baltimore said. “If you’re in high school, there’s just kind of immediate access to other people who are similarly situated. And I think people don’t feel like, ‘I was alone with nowhere to go,’ because of that.”

Thousands of underage migrants arrive in New York each year without their parents, often fleeing poverty or violence in their native countries. Many have formed deep bonds with Americans who do not want them to go.

In some cases, the bonds nurtured during high school extend after graduation.

Gerson Josué Santamaría Turcios, a 23-year-old recent graduate from Rhinebeck High School in New York’s Hudson Valley, arrived in the United States from Honduras almost six years ago. After high school, he built a landscaping business in the idyllic New York countryside, where neighbors treated him like family.

Mr. Turcios, who is undocumented, was detained after cutting the yard of resident Jenny Friedberg, who sounded the alarm for their friends to spring to action. Within days, a fund-raiser had amassed more than $100,000, including donations from Paul Rudd, the actor, and Andrew Jarecki, the filmmaker.

Soon thereafter, a charter bus and caravan of supporters traveled more than two hours to Manhattan in hopes a judge would keep Mr. Turcios from being transferred out of the city and into a Republican stronghold where he was more likely to be deported. Mr. Turcios has since been moved among several ICE detention centers, including two in Louisiana.

Outside the courtroom, his best friend, Brendan Dougherty, 20, said that he felt disappointed by his country.

“When I told him ICE was in Rhinebeck, I told him he could seek refuge at my house,” Mr. Dougherty said. “This kid had spent the past six years building a life here. I should be deported over him.”

For Joel Camas, the teenager from Ecuador, the future remains uncertain, his immigration case unresolved. His mother has returned to their homeland, deciding to leave rather than waiting to be deported by authorities. Joel remains in New York, still going to school.