Doctors say he died of a virus attack on his brain. His father, Mr Heng, 45, has his own theory, one based on emotion. He feels his son worked himself too hard, was too stressed, and this led to a coma, and death.
Heng Juan wanted to be first in everything, says Mr Heng, a graphic designer. He worried when he scored less than a distinction, as his journal showed. (See excerpts below)
Still, Mr Heng told himself his son was mature enough to be left alone. Until one day in November, 1993, after exams.
A virus attacked Heng Juan's brain. He slipped into a coma and died on Feb 10 -- just one day short of his 15th birthday.
Doctors say there is no medical proof that stress brings on encephalitis, the condition caused by the virus attack on Heng Juan's brain.
Voicing a general medical opinion, Dr Wong Meng Cheong, department head of Neurology at Singapore General Hospital, says: "The link is tenuous. Stress can suppress the immune system in some and you may be more open to certain diseases and infection. (But) if you and I get stressed, we are unlikely to come down with encephalitis the next day."
Mumps, herpes, chickenpox and cold sore viruses lead to encephalitis, a brain inflammation.
but even scientific fact has not stopped Mr Heng's brooding: "I want to tell students out there not to give themselves too much pressure. So long as you try your best your parents will be happy."
Heng Juan was a school swimmer and waterpolo player. In Sec 1 exams, he won awards for art, literature, being first in class and second in standard.
In Primary 6, he told his dad he would one day be a director of a well-known bank. One incident taught Mr Heng to believe this.
Students had been asked to list their target marks for an exam. Heng Juan confidently filled in "100" for science and maths. Father and teacher insisted he change it. He refused so his father had to alter the marks for him.
But Heng Juan scored 100 in both papers.
Adding that his son often came home too tired to eat, Mr Heng says, in an interview at their four-room flat off Serangoon Road: "I had to tell him not to study and to relax!"
At the end of 1993, Heng Juan was selected to be a prefect. Yet he was torn between that position and class monitor. Says Mr Heng: "He told me that if he was to do something, he would do it well or give it up."
His father does not know what choice he would have made -- he didn't have the chance to.
On Nov 17, he fell unconscious. He was warded at Tan Tock Seng Hospital, and later at the National University Hospital.
In July 1994, he was discharged, still in a coma. His condition improved gradually.
But in January, Heng Juan was admitted again with a ruptured artery. It burst again on Jan 31 and doctors tied the artery close.
On Feb 9, his condition worsened. Teachers and schoolmates stood vigil. The Hengs asked doctors to keep him alive just two more days -- his 15th birthday was on Feb 11.
But on Friday, his heart-beat grew erratic. At 3.30 pm, it stopped.
Madam lim Siow Eng visited her student almost every day to talk to him. More often, she spent hours encouraging his distressed parents -- either with words, or simply with her presence.
But a self-effacing Madam Lim, 55, who refused to have her photo taken, dismissed all praise with an almost embarrassed: "It was my duty."
She said she felt for his parents because, "as a mother, I knew how they would feel". Mr Heng noted she also came to treat Heng Juan "almost like he was her own son".
Madam Lim, the assistant head of the Chinese department, said she had been impressed with Heng Juan's sense of responsibility and concern for others.
She recalled how she had once confiscated a football, after the boys ignored a recess ban. Heng Juan pleaded with her.
"He explained that the boys wanted to release pent-up energy. He asked if they could be allowed to play during the first half of recess and then dry up before coming back into class. He said he would look after them," said Madam Lim, who later relented.
When Heng Juan finally went home, he needed a special bed for the infirm. Madam Lim asked around, and found a clerk whose friend had an old bed. She continues to visit the Heng home.
Like Madam Lim, friends and stranger who offered help taught us the meaning of love, said the Hengs.
They spoke with gratitude of the relatives, church friends, present and old school boys, teachers and members of the school's Parents Support Group who came forward.
Mr Heng said: "After Heng Juan got sick, I had no mood to work for months. I spent half my time looking after my son."
The hospital bills were mostly paid off with the help of social workers, the school, friends and strangers who had heard of their plight.
Added Mr Heng: "We only thought of living day to day, never of the years ahead. We really appreciate all the love and help that kept us going."