From the moment students file noisily into her honors physics class, Sister Claudette Naylor commands attention with a stately presence at the front of the classroom. The class settles down quickly and she begins the same way she does every day: with prayer.

She is the face of Catholic education at Holy Cross Academy in Delran, one of only two nuns remaining at the South Jersey parochial school, where more than two dozen sisters once were on staff. Across the country, the Catholic school landscape has changed dramatically, with enrollment dropping and schools closing.

Lay teachers now make up the bulk of Catholic school employees, a stark contrast to decades ago, when religious men and women — the vast majority nuns — composed 90 percent of school staff. Today, there are just 4,000 religious teachers, who represent 3 percent of all Catholic school staff from religious orders, according to the National Catholic Educational Association.

"The picture has changed completely," said Sister Dale McDonald, the organization's director of public policy. "For a lot of us, teaching was the only option. But as other options became available, people went into them."

At Holy Cross, Sister Claudette teaches three classes a day, often using an overhead projector with slides to illuminate her lessons. At 84, she has become a beloved fixture, teaching generations of students, with no plans to retire. Her students typically begin arriving for her first class at 8 a.m., before the bell, to spend time chatting with her.

"She's old-fashioned, but I like that about her," said freshman Whitney Daniels, 14, of Willingboro. "She has a caring personality."

Born in Chicago, Sister Claudette began her career in 1952 after entering the Sisters, Servants of the Immaculate Heart of Mary in Scranton. She has been at Holy Cross for 23 years, teaching primarily physics, biology, and math.

"I'm still having fun teaching. I'm teaching what I like," she said. "There aren't too many of us still around."

She resides with Sister Bernadette Thomas, a former business teacher who has been at the school for 30 years and now runs the media center. Nearly half of the 350 sisters in their order work in education.

"We don't look at this as a job," said Sister Bernadette, who has been teaching for nearly 50 years. "I don't go to work. I go to my ministry site."

Women who enter religious orders now have more career options outside the convent than the sisters of yesterday who took vows of poverty and were largely needed as teachers in parochial schools and worked for low wages. Even today, nuns typically earn less than their lay teacher counterparts.

Sisters who work outside the convent after taking their vows have expanded to fields that include health care; social services work with the homeless, AIDS patients, at-risk women and children, refugees, and immigrants; and spiritual ministries.

The decline in sisters among the teaching ranks can be attributed partly to a decline in interest in Catholic religious life. Since 1965, when there were about 180,000 nuns in the United States, the number has dropped steadily to about 45,000, according to the Center for Applied Research in the Apostolate. During that same period, the number of priests has also dropped, from about 58,000 to 38,000.

Meanwhile, Catholic school enrollment across the country has dropped from about five million in the 1960s to about two million students in elementary and secondary schools. It has become more common for students not to have a class taught by a nun, experts say.

"I can't think of a parochial school or high school that wouldn't want more sisters or brothers," said Maggie McGuinness, a religion professor at La Salle University. "Sisters in the schools were really the face of Catholicism that people saw."

In the region, the Diocese of Camden, which enrolls about 12,000 students in six counties, has 29 sisters working in elementary and secondary schools, down from 73 in 2007, the latest figures available. In 1975, the Archdiocese of Philadelphia had 1,963 religious teachers (sisters and brothers) in its parish elementary schools. That figure fell to 508 by 2001 and just 110 in 2016.

The Sisters of St. Joseph, one of the largest orders in the area, has seen its ranks drop in the past decade from about 272 sisters working in schools in 2008 to 118 this year. The population has also grown older, with the average age of teaching sisters rising from 71 in 2008 to 77.

On a recent day, St. Francis de Sales, a Catholic grade school with 500 students in West Philadelphia, hummed with activity. Sister Christine Lamb worked with a student learning English. Sister Francis Michael Finsterbush, the school's coordinator of finance and development, played chief cheerleader with a third-grade class working on an online math game. Sister James Anne Feerick delighted a small group of second graders reading a story about a frog.

The work is joyful, the sisters said, but they admit to feeling nostalgic for their early teaching days, when every class was taught by a nun. There are just six sisters among the teaching and administrative staff of 40.

"We love our ministry, and we wish there were more women coming to join us," said Sister Mary McNulty, the school's principal.

There's been a sea change since Rita Schwartz became one of the first lay teachers at St. Hubert Catholic High School for Girls in Northeast Philadelphia, in 1963. She heads the Association of Catholic Teachers, organized in 1963 to represent lay teachers at the city's 17 archdiocesan high schools.

"We were told that we were only there until religious vocations picked up," said Schwartz.

Nuns filled a critical need for teachers when Catholic education began in the early 1900s because Catholics believed their children were being discriminated against in public schools, said Bren Ortega Murphy, a women's studies professor at Loyola University in Chicago.

In their schools, the sisters helped shape the religious environment. Although few sisters in the classroom bear resemblance to the image of nuns in habits made famous in Sister Act, they give identity to their schools.

"They make a Catholic school a Catholic school," said Adelina Joseph, 17, of Mount Laurel, a senior at Holy Cross, the only Roman Catholic high school in Burlington County. "It wouldn't be the same without sisters."

The disappearance of nuns from Catholic education has had financial implications. When Sister Dale began her career as a teacher at a Catholic school in New York in 1961, her order, Sisters of the Presentation of the Blessed Virgin Mary, received a stipend of less than $800 annually for her work, and she lived in a parish convent.

The median stipend paid to sisters is now $30,000; lay teachers typically earn between $24,000 and $55,000. According to the National Center for Education Statistics, the average salary for public school teachers was $58,064.

At first, as fewer nuns worked in religious schools, parents were worried about the shift in the composition of the teaching staff. Some schools survived with few if any religious sisters; some closed, partly from competition from charter schools. An increasing number of Catholic schools have sought ways to reinvent themselves.

The four sisters who teach part-time at St. Basil Academy in Jenkintown diligently work with lay leaders to maintain Catholic traditions at the private girls' school founded by the Sisters of the Order of St. Basil the Great, said Sister Dorothy Ann Busowski. In 1985, nuns made up nearly half of the teachers.

Those numbers would have been unthinkable for the current students' mothers and grandmothers; to them, it's no big deal.

"Some of them don't even know what a sister looks like," Sister Dorothy said. "They're not in the schools and the parishes."

This year, Schwartz said, St. Hubert's in Philadelphia has no sisters teaching, though some work in support roles. John W. Hallahan Catholic Girls' High has five nuns, including two both in their 90s, who operate the school store, she said.

"It's really the end of an era," said Schwartz.

Though things have changed profoundly, Sister Barbara Buckley, the head of Merion Mercy Academy in Lower Merion, said she is glad to carry on a tradition that shaped millions of lives. Three nuns in the order work full-time in education.

"The strength of the Catholic Church was built on sisters who educated kids in the '40s, '50s and '60s," she said. "We all owe a lot to them."