With a weighty volume of physics open before him, Mark Sim is a picture of cherubic enthusiasm, turning pages and pointing out topics he is especially fond of.
"I like electricity, and oh, atomic physics because my dad explained to me how bombs work. Although I find the property of waves a little hard to understand..."
That caveat, tinged with child-like uncertainty, is a reminder that the soft-spoken Mark is just nine years old but already believed to be the youngest person in the world to score an A in the International General Certificate of Secondary Education (IGCSE) physics examination. The IGCSE is an internationally recognised qualification equivalent to the GCE O levels.
Mark was eight years and three months old when he took the exam - three papers over two days - at the British Council last November.
The feat earned him a spot in the Singapore Book of Records when it ratified his result with Cambridge earlier this year, said Mark's father, Mr Harry Sim Lim Onn, 48.
Mr Sim had wanted him to take the GCE O-level exam, but the Ministry of Education would not allow it. It imposes an age limit so parents do not put undue stress on their children. It cost Mr Sim $300 for his only child, now a Primary 3 pupil at Nanyang Primary, to take the exam.
Mr Sim, a permanent resident married to Singaporean Wun Ju Sing, 46, said Mark displayed a precocious talent for grasping basic physics concepts.
"I explained to him about acceleration and how my car differed from a Ferrari when he was six and he understood," said the section manager at a semi-conductor firm.
He subsequently bought Mark a physics textbook and the boy was hooked when told it was meant for students much older.
For a year leading up to the exam, Mark would study for half an hour every week day and up to three hours on weekends with his dad.
His feat mirrors that of Singaporean prodigy Ainan Cawley, who passed his chemistry O-level exam in 2007 at the age of seven.
It seemed quite the opposite for Mark in the beginning. "Our maid warned us not to expect too much from Mark; he could not even roll over on his own until he was nine months old," said Mr Sim.
Mark had to work hard for the exam. "His English was not very good and he had to make an extra effort in order to fully understand the questions," said Mr Sim.
Madam Wun, an accountant-turned-housewife, supervises his daily schedule and coaches him in English and mathematics. Mark was a member of the national junior chess squad, but he left last year to concentrate on preparing for the physics exam. He enjoys computer games and travelling, and he is also a huge fan of the film Minions.
"Mark has been getting attention in school, but we try to keep him grounded," she added.
There are plans for him to take the A-level physics exam in the next two years, although Mr Sim is wary of the demands of such an undertaking.
"Mark was the one who suggested it. He dragged me to the bookstore and made me buy the A-level physics textbook," he said. "We'll take it slow but he should have no problems scoring a B or C with the right preparation."