The woman was angry her daughter was being "picked on" the day she grabbed a 15-year-old girl by the hair and repeatedly punched her in the stomach during an altercation at Warrawong High School, Wollongong Local Court has heard.

The teen, who had gotten into an argument with the woman in the school car park, was punched a number of times in the head and stomach before falling to the ground.

The woman then punched a 14-year-old boy in the face, splitting his lip, as he came to the girl's defence.

Yesterday the court heard that just hours before the February 20 altercation, the woman and her de facto husband had been in the school office, complaining to staff that their daughter was being "picked on".

Giving evidence before the court, teacher's aid Cindy Dryden said she was in the office about 11.45am when she heard the couple's complaints during a heated exchange with staff.

"[The woman] said: 'If you don't do something, I will take matters into my own hands'," Ms Dryden told the court.

Less than four hours later, the Warrawong mother attacked the two children, leaving one semi-conscious.

Yesterday the woman pleaded guilty to one charge of affray before Local Court Magistrate Les Mabbutt.

Her de facto husband has pleaded not guilty to assaulting a school student while attending school, common assault and affray.

Police allege the man, who was present during the altercation between his partner and the children, also punched the 15-year-old on the head.

During the hearing yesterday, defence solicitor Bill Loukas argued "all my client did was try to break it up", saying none of the witnesses had seen him throw any punches.

However, teacher Ingrid Herringe told the court how she saw the man "grab [the 15-year-old girl] by the hair and 'reef' her side to side" moments after pulling his partner off the child.

Both matters were adjourned to today.