Police attended a primary school as a crowd of parents turned up to complain about how their children were disciplined following a Christmas concert.
The parents gathered at the gates of Windsor Clive Primary School in Ely, Cardiff, on Tuesday morning to speak to the headteacher.
Pupils had taken part in the school's Christmas concert at a nearby church on Monday morning and were praised in front of parents afterwards.
But after returning to school, the headteacher spoke to a group of pupils about their behaviour during the festive performance.
Parents claim children were branded a "disgrace" and told they would only have bread and water at their Christmas party if they did not improve.
Windsor Clive Primary School strongly denies the claims and refutes that children were spoken to in an "inappropriate manner".
Police attended the school after a crowd of angry parents asked to speak to the headteacher ahead of the second concert on Tuesday.
The school cancelled the concert, due to take place at 10am on Tuesday, due to the anger.
Some parents say their children were left in tears by the telling off, and will be kept off school until the matter is resolved.
Parent Craig Williams said they were "angered by such hurtful words" used to discipline the children, who were left "very unhappy and heartbroken".
"The parents didn't descend on the school like a mob, they politely requested that the said headteacher, who is one person everyone knows, gave us her time and explained to us why she felt the need to threaten and belittle the children," Mr Williams said.
"It has escalated to a situation where children don't want to go to school, a place where they have a right to be educated correctly.
"We are all writing letters to the chair of governors down in County Hall."
In a statement, a spokesman for Cardiff Council urged parents to complain through "appropriate channels".
"Some parents have alleged that, following the Christmas concert on Monday, pupils were spoken to in an inappropriate manner. The school refutes this," he said.