At New York City's Aquinas High School, helping the needy is both a commitment and a lesson. The students learn that . . .

Twice a week after classes, 20 girls bound out of Aquinas High School in the South Bronx, across Crotona Avenue, and through the front door of the Thorpe Family Residence, their white blouses and pleated skirts clashing with their hip-hop hairdos and Fu Manchu fingernails. They swing their bulging Sherpa backpacks off their shoulders and vanish down the hallways of the renovated five-story home for single mothers to play a game of Chutes and Ladders or change a diaper. It becomes clear very quickly that the students enjoy themselves as they give Thorpe's grateful mothers afternoons to themselves on a regular schedule.

So great is the enthusiasm for the Thorpe Big Sister program at Aquinas that 130 students signed up last fall to help Thorpe's 20 families. The overabundance of goodwill required program officials to hold a lottery to see which girls would be allowed to perform the highly coveted 80 volunteer jobs.

But being a Thorpe Big Sister is only one of many ways that the 812 students of the all-girls Catholic school reach out to the needy South Bronx community around them. Helping others is a central part of the educational experience at Aquinas, a school founded in 1923 by the Dominican Sisters of Sparkill, an order dedicated to social justice. The unofficial credo of the Sparkill order comes from Micah 6:8: "This is what Yahweh asks of you--only this. To act justly, to love tenderly, and to walk humbly with your God." And Aquinas's students accept this call to service.

Aquinas High School has a crucial but often neglected ingredient of educational excellence--a strong sense of shared purpose and community. Research shows that the more students feel they are embarked on a mission to which they are integral, the less likely they will feel alienated and fall between the educational cracks. "Students, as well as teachers, work harder when they feel connected, when they sense they belong," says Theodore Sizer, a leading school reformer. "They're more invested." Much as philanthropic groups and churches often find their highest purpose when members band together to serve others, so, too, high schoolers can bond with each other and their institutions by doing good works.

At Aquinas, the sense of community and the connectedness that it creates start with the school's Catholicism. Prayer and religious services suffuse the daily life of the school and that sends students a clear signal about what the school stands for. The school day begins with student-led prayers over the public-address system or via closed-circuit television. Many classes, like Jennifer Nugent's history course, also begin with prayers. Yet, while the school's morning prayers require students to stand silently at attention, Nugent's opening prayer ritual is warmer and more informal. Sitting at their desks, students might recite the Lord's Prayer together, pray for the victims of Hurricane Mitch, or individually petition for help with personal challenges like communicating better with parents. Airing those concerns gives the girls the sense that they are supported by their peers, says Sister Margaret Ryan, Aquinas's principal of 25 years.

The sisters at Aquinas themselves set a formidable example of the school's dedication to community service. Their order has helped bring affordable housing to what were vacant, crime-ridden lots near Aquinas. And it has run two Thorpe homes that provide services like short-term shelter and job training for homeless mothers and their children. "Catholicism and social justice are constitutive of who we are," says Sister Ancilla Maloney, who advises the school's 3H Club (Helping the Hungry and the Homeless). "It's not enough just to get good grades."

Hour by hour. That's a message students take to heart. Though the school encourages them to do 10 hours of service work a year, last year 60 percent of the 812 students exceeded the minimum requirement and 15 percent each performed more than 100 hours of service--and they did so while meeting the school's tough academic standards. At Aquinas, no one doubts that the two go hand in hand. "You want to do your best when you see what others don't have," says Cynethia Pena, a junior who volunteers at Thorpe by assisting a mother of six who dropped out of school after having her first child at 13. "You just have to go for that A when school's the hardest thing in your life." Indeed, helping the needy in the South Bronx has helped many Aquinas students to perform well despite their own difficult financial circumstances. There is scant evidence in the aspirations of Aquinas students to suggest that they face significant obstacles; 83 percent of them qualify for federally subsidized lunches. "We don't tell them they have to achieve against the odds or anything like that," says Sister Margaret. "We just tell them it's good to achieve."

The message Sister Margaret and her staff do send is that each student is important and that the school is behind them all. "We remind them constantly that this is a community of faith and learning and that they can do it because we know they can and because we're going to show them how," she says. Everything, it seems, from the school's single-sex atmosphere, rigorous admissions process, and challenging college-prep curriculum that allows little individual course selection, to the uniforms the girls wear, wraps Aquinas students in a web of shared experience designed to enhance their sense of belonging. "Every girl here knows what's expected of her, in terms of behavior and studies," says Sister Margaret. "There are no surprises."

In many sprawling public high schools teachers and administrators know students only superficially, Sizer and others say. But with her school's modest-size population, Sister Margaret and her faculty know a great many of their students by name, and they know the details of many of their students' lives. "I never even met the principal at my other school," says junior Flora Akosa, who spent her sophomore year at a Bronx public high school.

"If you cut class or didn't do homework, no one said anything. Teachers there can only care as much as you do; at Aquinas, they really want you to care."

Just ask for help. Aquinas makes it very difficult for student problems to go unnoticed. It's easier to address difficulties when they're caught early, the school believes. Every student takes a weekly course on life issues taught by one of the school's four guidance counselors, who lead discussions on subjects ranging from dating to college admissions. If students want to talk to a counselor individually they need only sign up for a same-day session. "And they do," says Sister Annmarie Fisher, head of the guidance department. "There's just no stigma to it." Says Aquinas senior Roseles Escano, "We'd talk about any problem we're encountering." Aquinas also has a tutoring system for students struggling academically.

The students develop strong ties to Aquinas. "It's a sisterhood," says Latasha Green, a junior, in a sentiment repeated by many of her classmates. "There's a 'Go Aquinas!' attitude you can't help getting into." This sense of sisterhood spans the generations of Aquinas students. Demographics have shifted over the years, from predominantly Italian and Irish (including Sister Margaret, who was born in the Bronx and graduated from Aquinas in the 1950s) to predominantly Hispanic and African-American today. Their loyalty to Aquinas is strong enough that many of the earlier graduates continue to make return visits to campus. Photographs from the school's 75th-anniversary celebration held last fall depict elderly white ladies lunching companionably with teenage Hispanic and African-American girls.

Students' sense of connectedness at Aquinas is such that many of the challenges that confront school leaders today simply do not exist at Aquinas. Attendance averages 96 percent each day, and 89 percent of the school's students participate in extracurricular activities. Despite the toughness of the South Bronx streets, discipline problems at Aquinas are negligible and fewer than 1 percent of students drop out.

The school's positive energy has helped produce powerful results in its classrooms--results that are all the more impressive given the financial struggles of many Aquinas families and the fact that the school admits students with a wide range of abilities. (It admits 90 percent of its applicants.) Some 43 percent of the school's seniors take courses for college credit in English, history, and Spanish. A local college, St. Thomas Aquinas College, approves Aquinas High School instructors to teach the college-level courses. Ninety-six Aquinas students attend college after graduating. Last year, 74 percent of the 185 students in the senior class went on to four-year colleges, while 24 percent attended two-year schools.

Among them, they earned $ 3.5 million in scholarships and grants to colleges and universities that include elite schools like Harvard, New York University, the University of Pennsylvania, and Cornell. In addition, the great majority of Aquinas students leave the school knowing how to play an instrument and read music.

Aquinas has advantages over most other schools in community building. Its loyalty to a religious tradition and the Sparkill order's devotion to helping the South Bronx lend themselves to the task. Being a single-gender institution makes the school "different" by definition and more homogeneous. Because Aquinas selects its students and, conversely, students select Aquinas, this sense of loyalty and community is inherent. The challenge for other high schools is to find their own ways of building community spirit--and giving their kids a sense that they have a stake in the whole enterprise.