He landed himself in a spot of trouble with the authorities twice for shoplifting.
And the idea of school irked him so much that he rarely showed up in class.
But Edmund Ng turned himself around and became one of his school's model students after scoring four distinctions when the O-level results were released earlier this month.
The Orchid Park Secondary School student now has a bigger plan: To further his studies in a banking and financial services course at Ngee Ann Polytechnic and one day start his own business.
Edmund, who was in the Normal Academic stream, said his divorced mother was the main reason for his change.
"I can't bear the sight of my mum being upset whenever she bails me out from the police station. I told myself that I needed to change now for the sake of my mum and my family."
The 16-year-old lives with his mother, Madam Lech Lee Poh, and two sisters in a four-room flat in Yishun. He said his rebellious streak began when he was in Secondary 1.
He had been introduced to a gang outside school who talked him into smoking his first cigarette and stealing beers from a convenience store in Yishun.
He said: "We were stealing beers from the fridge when one of us made a noise and the shopkeeper heard us. He called the police and we had to be detained in the police station for more than four hours."
Edmund said he could not forget how crestfallen his mother was when she arrived at the police station to bail him out.
He also recounted that he had been caned 13 times in school within three years for starting fights, smoking in school and defying his teachers.
At the start of Sec 4, Edmund felt compelled to change.
It was sparked by a phrase his principles of accounts teacher, Mrs Adeline Yeo, told the class during a lesson: "If not you, then who? If not now, then when?"
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