The call from her husband first had Madam Nurhafizah Abdul Aziz worried as she thought her son had been injured in a fall.
But her worry quickly turned into anger when she found out what had happened.
Their son, Muhammad Azief Rashdyn, nine, had been slapped by a classmate's father during his music lesson.
What made it more shocking was that it happened in the presence of his teacher and other classmates.
The man had slapped the boy for allegedly bullying his daughter. Both are pupils of Clementi Primary School.
"My son was so traumatised by the incident that he wet his shorts. He didn't dare tell his teacher about it," Madam Nurhafizah, 34, who works in a childcare centre, told The New Paper yesterday.
The incident happened on Wednesday.
Madam Nurhafizah said she and her husband rushed down to the school, where the principal told them what had happened.
When she got to see her son shortly after, Azief had an ice pack on his swollen cheek and complained of pain.
"I was shocked that the palm-shaped bruise was clearly visible on his left cheek. As a parent, I would never lay my hand on my sons.
So what right does that man have?" said Madam Nurhafizah who has another son, a 13-year-old.
According to what Azief had told her, he was not sure what he had done wrong, she said.
He could recall only one occasion in school which might have upset the female pupil, who is a fellow classmate, Madam Nurhafizah added.
Her son and the girl were both walking in the same direction when she allegedly turned to him and accused him of following her, he said.
Said Madam Nurhafizah: "My son is playful and he may have joked with her (the female student) in class. But if you have a complaint, you should inform the principal or talk to me.
"As adults, we should not take matters into our own hands, especially when it concerns other people's children."
She and her husband have since made a police report.
The police have confirmed a report was made and that they are investigating the incident.
Madam Nurhafizah related what happened that day in class, as told to her by her son.
According to him, the music lesson had already started when the man came knocking at the classroom door.
The female teacher appointed a pupil to open the door. The man then entered the classroom with his daughter and loudly asked who had bullied her.
Azief heard his name being called out by the man. The girl had supposedly pointed him out.
According to Azief, the man then asked him to step forward.
He claimed that when he hesitated, the man shouted: "You, come here!"
Azief said he walked slowly towards the man, thinking he just wanted to talk.
He was shocked when the man allegedly slapped him - in front of the whole class, with the music teacher standing nearby.
Almost immediately, the teacher protested and told the man to leave. She then asked her pupils to get help.
The incident has also upset Azief's aunt, who gave her name only as Ms Zulyana.
She was baffled that nobody had called the police.
Ms Zulyana, 29, a teacher, said: "I am surprised why the parent was allowed into the classroom. As a teacher, if anybody shouts at my students in class, I would tell him to leave immediately."
Two days after the incident, Azief has regained some confidence and is starting to behave like his jovial self.
When he was interviewed at the police station and examined at a polyclinic on the day of the incident, he was reluctant to relate the incident to strangers.
Said Madam Nurhafizah: "We are not bringing up the subject to him because we hope he can focus on his exams which start on Monday."
SCHOOL DOES NOT CONDONE PARENT'S BEHAVIOUR
The principal of Clementi Primary School, Mr Albert Chia, told The New Paper last night that the school had looked into the matter.
It had also followed up with the girl's father, as well as Muhammad Azief Rashdyn and his parents.
Said Mr Chia: "Such behaviour from parents is not condoned. We urge our parents to work with the staff to resolve any issues among students."
It is understood that the girl's father had entered the school and told the security guard he was seeing the principal.
Instead, the man went to one of the classrooms where the students were having music class.
When the slapping occurred, the music teacher intervened and prevented the man from coming into further contact with Azief.
TNP understands the man had been dealt with by the school. He feels remorseful and is willing to apologise to the boy's parents.
Lawyers told TNP that Azief's parents may be able to seek legal redress by filing a magistrate's complaint.
The act of slapping may be classified as voluntarily causing hurt to Azief, said lawyer Josephus Tan.
Lawyer N. Kanagavijayan said the issue of trespassing can also be considered against the man.
Said Mr Kanagavijayan: "The moment the man committed an undesirable act in the school premises, and he did not leave when told to do so, then he can be said to have trespassed."
This article was first published on October 10, 2015. Get The New Paper for more stories.