The century-old building, which fills most of a city block in the heart of Hasidic Williamsburg, Brooklyn, holds 15 first-grade classrooms, each with as many as 28 students.
Despite the building's massive size, the school has had to open an annex down the block for its youngest students, the high school is in a different location and a new building with 40 additional classrooms is being built across the street.
In total, 2,900 girls attend Bais Rochel, which provides education from preschool through high school.
"We are building just to breathe for the next seven or eight years," said Rabbi Hertz Frankel, Bais Rochel's English division principal.
The ultra-Orthodox "community grows by almost 30 percent every generation of 18 years," said Zalman Alpert, a reference librarian at Yeshiva University and an expert on the Haredi community.
At Bais Rochel, the population explosion is palpable.
There are 10 classes of eighth graders, 15 classes of first graders and 16 classes of preschool girls, and classes being added every year, says Frankel.
He received three years probation and the school paid a $1 million fine.
Since that time the population boom has continued unabated. "People used to talk about [families having] an average of seven children. Now they talk about nine," Frankel said.
Keeping up with the demand is challenging every school serving a Haredi community, said Devorah Yudkowsky, executive coordinator and director of student placement at Torah Umesorah.
"They really are keeping the pace and building to suit. But I still can't get children into a lot of the schools because there's no room. Most of the schools are bursting at the seams."
In Lakewood, N.J. alone, 14 new Jewish schools opened this month, she said.
In Crown Heights, the world center of the Lubavitch community, "All the schools are struggling to keep up with demand," said Eli Cohen, executive director of the Crown Heights Jewish Community Council.
"Space and money to build are in short supply." One of the ways ultra-Orthodox communities have responded is by building new schools beyond the boundaries of their neighborhoods.
"All of the new yeshivas and girls schools are built on the outskirts, beyond the eruv map," the boundary demarcating where Orthodox Jews are permitted to carry items on Shabbat, said Alexander Rapoport, a father of six and the founder of Masbia, a food pantry.
Eitz Chayim, a new boys' elementary school for Borough Park Hasidic families, is located in nearby Bensonhurst due to space constraints, said Yidel Perlstein, president of Eitz Chayim's board.
"We have a real-live yard and big lunch room," said Perlstein. "It was worth it to come 10 or 15 blocks out of the area to fulfill what we need."
Lowest tuition in the U.S.
At Eitz Chayim tuition is $3,975. The low fee "is our number one problem," Perlstein said. When families have three, five or even more children in a given school at any particular time there is a limit to what they can pay.
"There's no possibility most members of these communities can pay more. If you have between 8 and 12 children, how are you possibly going to pay $10,000 to $15,000 in tuition a year" per child, said Yeshiva University's Alpert. "They have to keep it low. I don't think they have an alternative."
Instead, the schools and their staffers make do through a kind of shadow economy, where people rely on donations of money, goods and services from within Haredi communities and public assistance programs for things like health insurance.
At Eitz Chayim, "The school is all donations. We have a group of parents, they help," Perlstein said. For example, "we needed electric outlets put in and a parent sent his guy" to do it. The school's rent is more than $15,000 per month.
There are "no benefits. No health insurance. We try wherever we can to help them out," said Perlstein. We are "giving out shoes, vouchers, food before a holiday."
"At the end of the day, we'll see what our shortfall is. We'll do dinners, have the kids sell raffles, have different ladies parties to raise as much as we can," he said. "If that doesn't work, we reach out to individual people, to grandparents, to help us keep the school open."