"I would like to give you some homework. Can I do that? It is a simple request, but very important," he told them.
"Please don't forget to pray for me, so that I can share with many people the joy of Jesus," he said. "Let us also pray so that many people can share the joy like yours."
And joyous they were. When Francis arrived, dozens of school children were lined up outside of the school. At a beauty shop across the street, about 30 people who had been waiting since last night held up banners and scream out his name in Spanish: Francisco, Francisco!
The students squealed and some shed tears of joy while taking selfies with the Pope.
"They tell me that one of the nice things about this school ... is that some of its students here, some of you, come from other places and many from other countries," Francis said. "That is nice!"
The school, which serves 295 mostly Latino and black children, is in line with Francis' mission of serving immigrants, the marginalized and the poor. It also illustrates the Roman Catholic Church's struggles with changing times, diminishing congregations and a dwindling priesthood.
Students from other schools were also in the audience.
Patrick McAvoy, 17, a student at Albertus Magnus High School in Rockland County, handed the Pope a small bag with religious metals he wanted blessed by the Pontiff.
Nicholas DiGrandi, 18, of Kennedy Catholic High School in upstate Somers, New York, asked the Pope to bless a photo of an aunt who died of a brain tumor one year ago.
Christopher Diaz, 12, a student at Our Lady Queen of Angels School, was sweaty after waiting outside for hours for the pope to arrive. "I wasn't sweating anymore after seeing his smile," he said. "He took my hand."
He asked Francis to pray for his father. Christopher was still emotional after the papal motorcade left.
"I think I will feel like this forever," he said. "I got to meet the Pope."
Francis told the students school can become a second home -- "one big family for all" -- where students learn to help each other, work as a team, and pursue dreams.
For the third time since arriving in the U.S., Francis referenced Martin Luther King. "It is beautiful to have dreams. It is beautiful also to be able to fight for those dreams. Don't forget about that."
The students showed him how to use a touch screen, which seemed a bit out the comfort zone for the man who's never owned a cell phone.
After visiting with the students, the Pope met with immigrants and received gifts, including tools from day laborers, and a book with immigrants' stories.
Ariel Mejia, 18, who one year ago arrived in the United States as an unaccompanied minor after crossing the Mexican border, presented Pope Francis with a soccer jersey. Another young man gave the pope a soccer ball. Then they put on a little soccer display for the smiling Francis.
"He said he would pray for us and asked us to pray for him," said Mejia, who is from Honduras.
In a historic address to Congress on Thursday, Francis asked lawmakers to embrace millions of undocumented immigrants.
"We, the people of this continent, are not fearful of foreigners, because most of us were once foreigners," he told lawmakers, military brass, Supreme Court justices and Cabinet members.
"We must not be taken aback by their numbers, but rather view them as persons, seeing their faces and listening to their stories, trying to respond as best we can to their situation."
In addition to the East Harlem stop, the Jesuit Pope's itinerary included time with homeless people in Washington. Francis will also visit prisoners in Philadelphia.
"He's an instinctual politician and the people he relates to are those he regards as the most fragile," said Margaret Crahan, director of the Cuba program at the Institute of Latin American Studies at Columbia University.
"His persona is very much linked to relating to people in a very direct fashion. ... And he derives warmth from children."
In a classroom at the Manhattan school, where nearly 70% of students are Hispanic and 22% black, the children will sing for the special guest -- himself a son of immigrants. They will pray and talk about community service and the environment.
The visit comes at a time when New York has shuttered dozens of parochial schools in recent years in part because of demographic changes and diminishing enrollments.
"I hope his visit fundamentally changes the conversation about Catholic education in America," said Kathleen Porter-Magee, superintendent and chief academic officer at the Partnership for Inner-City Education, which manages Our Lady Queen of Angels and five other schools in the Bronx and Harlem.
"The headlines have been largely negative over the past several years ... People have talked about schools closing and struggling and Catholics moving out of the city to the suburbs. That's really put pressure on the schools, particularly those that serve our neediest students."
Before his visit to the school, Francis addressed a global stage at the United Nations. He presented himself as a champion of the poor and suggested solutions for leaders to adopt to combat war, environmental destruction and poverty. Francis also joined an interfaith prayer service at the ground zero memorial.