A 21-year-old student who was already serving a jail term for cheating a supermarket chain of $500,000 in shopping vouchers has been spared reformative training.

This was after Justice Choo Han Teck on Friday threw out an appeal by the prosecution for Hakim Leong to undergo the training and decided to let him serve out the remainder of his 81/2-month term.

Reformative training is a regime in which offenders below the age of 21 are detained at a reformative training centre for between 1½ and three years, as they undergo structured rehabilitation programmes.

If Justice Choo had agreed to the appeal, Leong would effectively have to start his sentence all over again as the three months he had already spent behind bars for pulling off the scam in 2011 would not count.

The prosecution had filed the appeal, saying reformative training should take precedence over a jail term considering Leong's age and the amount involved.

Deputy Public Prosecutors David Chew and Grace Lim had argued that this was the "last chance" to reform Leong, who had been the mastermind behind the scam.

But Leong's lawyer, Mr Lee Teck Leng, questioned the fairness of sentencing Leong to reformative training, arguing that the total loss suffered by NTUC FairPrice had only been about $6,000.

After turning down the appeal, Justice Choo had this warning for Leong: "If (Leong) does not amend (his) clear defects and re-offends, he will face a much longer time in prison", adding that the matter was in Leong's own hands.

Together with an accomplice, Leong had set up a company in November 2011, for the purpose of buying the $500,000 worth of shopping vouchers with a dud cheque.

Some $13,180 worth of vouchers - and not $5,000 as earlier reported - had been spent before the cheque bounced and he was arrested.