Kelly Mochan stormed into the school swearing and shouting that she was going to kill Katie Vincent, as other mums picked up their kids, The Sun reported. She was carrying a baseball bat.
Vincent, 31, had actually sent her mother Tonia Vincent to collect her children on that day from the school. So a furious Mochan clubbed her with the baseball bat in front of scared youngsters.
The 53-year-old grandmother was smashed on the head. She required hospital treatment after teaching assistants pulled the two women apart.
Mochan had some of her children with her at the time of the attack in the car park at the school near Bridgend, South Wales.
Prosecutor Mike Hammett said: "She told the gran: "I'll get your f****** daughter" as she was going through the car park. There was an exchange of words and she said she was going to kill Katie for what she had done.
The grandmother later said: "The doctors told me I had a very lucky escape. She was a lunatic. A mother of six should be ashamed of herself for behaving like that.
"I just hope she gets treatment for her anger - she needs it badly."