Mr Chester Ong's old school, Bukit Merah Primary, no longer exists. It closed at the end of 1997 and he was the head prefect from the last batch of pupils.

There was no social media or mobile phones then, says the public servant. Apart from a few of his closest friends, he has lost touch with others in his primary school.

But a chat with a friend in 2013 inspired him to create a Facebook page for former schoolmates to get together. Mr Ong, 31, who is now married with a nine-month-old son, says: "As head prefect, I felt I had a responsibility to start a platform for people to reconnect."

Turning to his old autograph book, where schoolmates had written their telephone numbers, he rang some numbers and found some schoolmates. "Others had moved away, but their parents, or the new owners of their flat, helped me get in touch with them."

Most of them were happy to catch up. They started a chat group on WhatsApp and nine of them met for dinner some months later. They now meet in restaurants or at someone's home every other month to reminisce about old times.

The ties that bind certain groups of old classmates can be strong, but may not necessarily survive the years. But with social media, more alumni are reconnecting over Facebook and WhatsApp and organising reunions.

In fast-changing Singapore, where some of these schools may be gone - either closed or merged with another school - these meet-ups are all the more poignant.

Ms Joanna Yong, 31, one of Mr Ong's former classmates and now a senior business development manager, says they had a blast at their first meeting. They laughed about the nicknames they gave one another and who their favourite teachers were, and shared tidbits about their personal lives.

She adds: "I went there hoping to re-establish those lost friendships and I am glad I did."

Their former discipline mistress, Ms Yeow Chiok Fun, in her late 60s, was also present at the meeting.

Ms Yong says: "We were impressed that she remembered most of our names and the naughty things some of us did, such as putting glue on chairs, shooting paper bullets at others and cutting a hole in the fence to escape from school."

The group has been meeting every other month for a meal or drinks. Their Facebook page has 294 "likes" from former classmates and schoolmates.

Some of the alumni from the former Woodsville Secondary, which merged with MacPherson Secondary in 2004, are also as thick as thieves.

Mr Thomas Lee, 48, who graduated in 1986, started a Facebook group - Woodsville Sec Class - last year, which now has more than 30 members.

Tracking down his classmates was not easy, says Mr Lee, now the manager of cleaning company Friendly Supplies. He is married with two sons, aged 22 and 16.

"On Facebook, many do not go by the names they used in primary school. They also look different."

Even after finding the right person, he found that some were not keen on re-connecting. He says: "They said that since we have not been in contact for so many years, why start again? Some did not even remember me.

"Their comments demoralised me, but I pushed on because I knew many others were excited about meeting again."

Eight schoolmates eventually met at a Burger King outlet to organise a larger gathering, which was attended by more than 50 schoolmates and 10 teachers.

Housewife Annie Choo, 47, who attended the gathering, says: "It was our first reunion in 30 years and I thoroughly enjoyed meeting old friends and recalling the good old memories we shared.

"And the fact that our former teachers were there made it all the more memorable."

One of the teachers who attended the reunion was their former form teacher, Mrs Lee Lai Kiong, now 73. Says the retired Chinese teacher: "When Thomas invited me, I was so happy and excited. I care for my students like my own children."

During the meeting, she adds, some former students were so happy to see her that they hugged her. Many asked if she recognised them or remembered their names.

"To be honest, each class has 40 students, so I am usually able to remember only the names of those who are very good or very naughty.

"It's very heartening that they took the initiative to keep in touch. It shows that as teachers, we have taught them well."

For Dr Victor Tay, 45, an alumni of Alexandra Estate Primary, which merged with Jervois Primary in 1988, keeping in touch with his primary school friends lets him relive the happiest years of his life.

He graduated in 1982, but still meets them at least twice a year.

Now a vice-president of the Asso- ciation for Persons with Special Needs, he says: "My primary-school days were so carefree and simple. My friends and I would play marbles and catch fish during recess or after school, and we thoroughly enjoyed ourselves.

He recalls that his friends used to think an abandoned mansion near their school was haunted. They once walked into the place after school.

"It was silly, but fun and thrilling," he says. "During our meetings, we look back at such incidents and have a good laugh."

What some former schools have become...

HOME TEAM CAREER CENTRE

Address: 178 Neil Road

Former occupant: Fairfield Girls' School

In 2000, it was conserved by the Urban Redevelopment Authority and restoration plans started in 2010. The building's external brick facade is original, but the roof, the central timber staircase, doors, windows and floorboards have been replicated and replaced.

Features such as mouldings, keystones and timber trimmings were also touched up and repaired to restore the "charm and allure" of the century-old building.

PEOPLE'S ASSOCIATION HEADQUARTERS

Address: 9 King George's Avenue

Former occupants: Victoria School from 1933 to 1984, Christ Church Secondary School from 1985 to 2001

This site has been the headquarters of the People's Association since 2009. The location was given a $47-million makeover, according to a Straits Times report in 2010.

The classrooms were converted into offices and the school hall- cum-canteen was turned into a dance studio and storage area for Chingay and National Day props.

CHONG WEN GE

Address: 168 Telok Ayer Street

Former occupant: Chong Hock Girls' School

The building is owned by the Singapore Hokkien Huay Kuan.

Since 2015, it has been rented out to the Singapore Musical Box Museum, which showcases antique musical boxes dating back to the mid-18th century.

Next month, a gallery featuring Peranakan tiles will open on the first level. There will also be a teahouse in this gallery. Admission to the museum is $12 for adults.

ALIWAL ARTS CENTRE

Address: 28 Aliwal Street

Former occupant: The former Chong Cheng School for boys and Chong Pun Girls' School, which eventually merged. The school closed in the 1980s

In 2011, the building was conserved by the Urban Redevelopment Authority.

It is now a three-storey multi-disciplinary arts centre, home to 15 arts groups and organisations as well as two restaurants.

The building has facilities for rent including a music studio, performance space, storage rooms, multi-purpose rooms, shared office workstations and lockers.

JAMIYAH CHILDREN'S HOME

Address: 15 Guillemard Crescent

Former occupant: Guillemard East Primary School

According to the Jamiyah's website, it aims to shelter and provide a proper upbringing to underprivileged children. These include orphans and neglected children of single parents, drug detainees, abused families, and those with special needs.

WANDERLUST HOTEL

Address: 2 Dickson Road

>Former occupant: Hong Wen School from 1945 to 1981

This four-storey Art Deco-style building has been a boutique hotel since 2010. There are 29 rooms and a French restaurant.

The second floor, which used to be a rooftop playground for students, is now a hot tub.

Most of the external architectural features, including the intricately painted ceramic tiles on its front facade and the classic stained-glass windows on the upper floors, have been restored.

CHINESE DEVELOPMENT ASSISTANCE COUNCIL BUILDING

Address: 65 Tanjong Katong Road

Former occupant: Yock Eng High School from 1941 to 1985

Since 1994, the building has been the headquarters of the council, which aims to nurture and develop the potential of the Chinese community.

One of the council's 13 centres is housed in this building. Tuition classes and enrichment programmes are held for students from lower-income families. Beneficiaries apply for bursaries, fee subsidy schemes, hardship assistance schemes, workfare programmes and other financial support schemes here.

There are also talks, workshops and IT courses for the elderly.

NATIONAL DESIGN CENTRE

Address: 111 Middle Road

Former occupant: St Anthony's Convent Primary School and Secondary School

Since 2013, this building has been an integrated hub, housing the DesignSingapore Council, design companies, prototyping and tinkering laboratories and a design store.

It is open to the public and has facilities for the design community to hold workshops, seminars, exhibitions and events.

The former school canteen is now a reception area, the former school hall is now a design store and the former teacher's room and science laboratories are now exhibition spaces.

RED CROSS TRAINING CAMPSITE

Address: 62 Jalan Khairuddin

Former occupant: CHIJ (Opera Estate) Primary School

The Singapore Red Cross has occupied the building since 1991. Camps and team-building and training activities, including those that teach life-saving skills and how to respond during national disasters, are held there. Logistics preparation for big-scale youth events is also held there.

It has a thrift shop, with proceeds going towards sustaining the Red Cross' local programmes.

The former school's canteen is now a meal hall where meals and snacks are served during youth camps and training sessions.

ASCOTT CENTRE FOR EXCELLENCE

Address: 2 Anthony Road

Former occupant: Chao Yang Special School from 1986 to 2005

Since 2007, this building has been the global hospitality training centre of The Ascott, a serviced residence business wholly owned by CapitaLand.

Training programmes focusing on topics such as operational readiness and service excellence, are held at this 12,000 sq m venue. To date, more than 14,000 hospitality professionals - Ascott staff and clients from more than 20 countries - have been trained here.