A teenage boy got to know an underage schoolmate in February 2018 before meeting the 13-year-old girl four months later at a staircase landing, where he forcibly placed her right hand over his exposed private parts.
When the minor did not reciprocate his actions, he told her that she had "wasted his time" and left.
He later befriended a second 13-year-old girl and lured her last February to another staircase landing, where they had sexual intercourse.
The 17-year-old was sentenced yesterday to 21 months' probation after he pleaded guilty to one count each of sexually penetrating a minor and causing a child to hold his private parts.
He must also perform 150 hours of community service, and his parents were bonded for $5,000 to ensure his good behaviour.
He cannot be named as a gag order has been imposed to protect his victims' identities.
Deputy Public Prosecutor Angela Ang said that the offender and the first victim were in the same co-curricular activity (CCA) in school in 2018. Court documents did not reveal details about the CCA.
The pair went to a staircase landing in Woodlands in March that year and started kissing. The girl felt disgusted when he later made a lewd remark, and they quarrelled before he left the vicinity.
Despite this, they met again at the same staircase landing in June 2018 and started chatting.
The court heard that he suddenly pulled down his trousers and placed her hand on his genitals.
The girl froze as she did not know what to do, and he left in a huff after accusing her of wasting his time. She told a friend about what had happened, and the police were alerted.
The youth started chatting with his second victim through Instagram last January, and he later sent the 13-year-old girl a picture of his private parts.
The prosecutor said: "The victim then sent him a photo of her chest, with her clothes on. The accused then requested for a more 'open' photo... The victim then took a photo of her naked chest, edited it to blur it, and sent it to the accused."
On Feb 25 last year, he lured the girl to another staircase landing in Woodlands and had protected sexual intercourse with her. He continued with the act even though she was crying in pain, the court heard.
The next day, she told one of her seniors in school about her ordeal, and a police report was made on March 1 last year.
Offenders convicted of sexually penetrating a minor below 14 years old can be jailed for up to 20 years and can also be fined or caned.