A mother repeatedly punched a teenage girl she accused of bullying her daughter, a court heard.
Mum-of-four Nicola Young, aged 33, confronted a group of children outside the school gates, Plymouth magistrates were told.
The 15-year-old girl tried to push her away but Young punched her several times and pulled her hair.
Her solicitor said the single mum lashed out because her 11-year-old daughter had been teased about her weight and bullied for months.
Alan Harris said the girl's father had complained to the school but the parents did not think staff were doing enough to tackle the problem.
Young, of Chatsworth Gardens, West Park, admitted assaulting the girl by beating her on December 2.
Magistrates imposed a 12-month conditional discharge, ordered her to pay £50 compensation to the girl and £200 towards prosecution costs.
Michael French, for the Crown Prosecution Service, said Young drove to pick up her daughter from her school that afternoon.
He added the girl pointed out a group of students responsible for bullying her.
Mr French said Young left the car so that it was blocking the road and 'angrily approached' the group of students.
He added Young accused them of bullying her daughter, directing her comments at the tallest lad in the group.
Mr French said the 15-year-old girl stepped forward and said Young should report the problem to staff.
He added Young continued to shout angrily until the teenage girl pushed her away.
Mr French said Young punched her 'a number of times' in the face and pulled her hair.
He added the teenager was left with bruises and marks to her face.
Mr French read from a statement from the girl which said: "I am scared to go out by myself in case I encounter Nicola Young."
Alan Harris, for Young, said she had four children ranging from 20 months to 17 years and had no previous convictions.
He added: "The 11-year-old has been subjected to persistent unpleasant comments and then bullying because she is perceived by other children as being slightly overweight."
Mr Harris said the girl told her mother, who told her to stay out of the way of the bullies.
But he added that even if she went to the edge of the school grounds, the bullies found her.
Mr Harris said: "The insulting jibes continued. For example, they would ask her how she got on in her spelling test and then say to her 'not very well, because all you can spell is KFC'."
He added the girl's father met staff because he was worried about the bullying but the problems continued.
Mr Harris said Young accepted she caused the girl's injuries and had over-reacted.
The court heard that the 11-year-old girl has since been moved to another school.