It is 9.30am and a constant flow of pupils have already been through the door of the glass office of Rachel Cohen on the sprawling Boys Town Jerusalem campus. And many of the requests she deals with are not standard school secretary fare.

Because for the 900 boys between the ages of 12 and 20, "we are not just a school. We are their home, their social services, their mother, their father - we are everything." As she is speaking, a group of students arrive, all clutching 200 shekels (£40) to secure their place on a summer programme.

Boys Town was established in 1948 as an orphanage for young Holocaust survivors and immigrants. Today its intake is largely from low socio-economic backgrounds and 350 of the older pupils live on the 18-acre campus in the Bayit Vegan neighbourhood and are provided with three meals a day.

"Our students come from divorced families,where the parents don't work or where there has been physical abuse or sexual abuse in the family," Mrs Cohen explains. "They can be one of 10 children living in a two-bedroom flat. There is no food at home and they go hungry. So they need another place to call home."

The 200 shekel contribution will allow boys to live, eat and study at the school through the summer holiday period. "Many have asked us if they can stay at school because they have nowhere else to go. So we have come up with this programme. The 200 shekels is all we ask from them and we will come up with the rest needed to fund their stay."

Boys Town receives state funding to operate between the hours of 8:30am and 1:30pm. It relies on charitable support from the diaspora to keep it functioning as the 24/7 institution it prides itself on being.

Yoni Strimber, its international development executive, reports that "it costs us £7 million a year to provide a home and education for these boys.

"In other schools, the children go home but here they stay seven days a week if they want to. We run education to 8:30pm and provide them with three meals a day. We have to raise £4 million a year just to keep going. At the moment, most of that comes from the US."

As an example of the background of pupils, Mrs Cohen cites the case of Yossi, one of those staying for the summer. "His father can't afford to look after him and his mother is dead. So he cleans floors in his spare time to help his family."

Mrs Cohen, who has worked at Boys Town for 29 years, says that 75 per cent of pupils face comparable hardships.

Another pupil arrives at her door. Before he can speak, she takes a belt out of her draw and hands it to him.

"We help them with clothes, too," she says. "We get clothes donated for them. I keep things aside as they always come to me for help."

As well as providing a home and education, Boys Town is one of Israel's leading technological training centres.

Many of its 7,000 alumni have gone on to become engineers and technicians for the army, or work for market leaders such as Cisco and Microsoft.

The office of Yossi Lavi, head of the education department, is flanked by two classrooms with seemingly endless rows of hi-tech computers. He says "it is very rare that you will find a school that will take any child regardless and turn them into future leaders in the field".

On his wall are pictures of the school's founder, Brooklyn-born Rabbi Alexander Linchner, and an IDF plane.

Pointing to the image of the plane, Mr Lavi, an educator for more than 40 years, adds: "The army like what we do so much they are pushing other schools to open similar programmes.

"Our students are working on engineering that helps the air force and they end up working on technology that supports the Iron Dome."

Boys Town's College of Applied Engineering was established in 1971 in partnership with the IDF.

"Students who show promise in engineering receive a two-year deferment from military service and then go on to serve in the IDF as applied engineers.

"The IDF like it because they are getting the best people. And when you take into account the background of the children who go here and the fact they don't pay a penny for what we offer, it is really unique."

Three years ago, Yehudah was part of the school's award-winning robotics team for 13 to 14-year-olds.

Today he walks around the robotics lab with pride, while explaining how he helps to mentor fellow pupils.

"My family originally came from the USSR and when I found out about this school I was very excited," he recalls.

"It was the only school that had robotics. I love coming here because I don't have to take food from home and I can stay here.

"It has a lot of resources and if you are a good student, you are looked after. You don't feel suppressed here and bad things don't happen."

His robotics teammate, Elazar, 16, agrees. "We get three meals a day here and that means a lot. I don't get that at home. I like learning to build things and present them. Robotics is something I would like to go into in the future and this is a good school for that."

He also enjoys the school's diversity, with the family roots of the student population traceable to 45 countries on six continents. Walking through corridors echoing to the noisy chatter of his peers, Elazar adds that he has "friends from everywhere - Ethiopia, Iran, Morocco, France. Our school shows us that we are all the same."

That pupils embrace their shared heritage is important to maths teacher Doron Teib.

Mr Teib takes boys on an annual trip to Poland to understand the Holocaust. "Most of the students here have no direct family connection to the Shoah," he explains. "They come from places like Morocco or Tunisia and there is a culture in some Sephardi families to say: 'Well that didn't happen to me.'

"It is our job to help them understand we have a large survivor community here and it is what the school was founded on.

"We also arrange volunteering opportunities for the students," says Mr Teib, one of 130 graduates who have come back to work at Boys Town.

"We encourage them to be active members in the community. They go to old people's homes and help to pack food for soldiers. It is important to give back and understand that it is a part of being Jewish."

Mr Strimber is proud that an "intense enrolment process" with support from Jerusalem municipality social services has limited the number of drop-outs - they account for just one per cent annually. "And BTJ will not allow a boy to leave its embrace without making sure they have a suitable alternate solution."

For its alumni, contact is maintained through social media and e-newsletters. Staff members visit them regularly at their army bases and each class holds six reunions throughout the year.

Waving a handful of invoices for vegetables, Tova Rottenberg, head of the food services department, says she has become a hard-nosed negotiator in her 16 years in the role. For 3,000 meals have to be provided on a daily budget equivalent to just £4,771.

"I call round everywhere to get the best prices. I argue and that takes time.

"We are not like a normal school just serving lunch. We are the mother cooking three times a day for her family.We know these are the only meals that many of our students will eat. Their homes are empty so they need our food to make them fit and healthy to concentrate on education."

Back in the secretary's office, Mrs Cohen, a mother of five, says it is easy to appreciate pupil needs when you treat them as your own.

"So I've got 905 children. I think we all feel that way about our boys."

Her voice quivers as she reaches for the box of tissues on her desk.

"I need these for me and them," she explains. "One of the kids who asked me if he can stay at the school this summer lives in the Negev.

"His father is in jail for drug abuse and the mother can't work. He wants to be able to stay here so he can work in Jerusalem and send money back to the family. These are the kind of boys we have in the school."