A mother has been banned from her daughter's school after assaulting a 13-year-old girl she believed was a bullying her teenager.

Mother-of-four Sally Burnside had assured the principal she wouldn’t attack the teenager but was filmed assaulting her on school grounds soon after.

The 35-year-old from Glenroy had gone to the Murray High School in Lavington, just north of the Victoria-NSW border, to talk about the apparent bullying her daughter had been subjected to, but ended up attacking the teenager.

“It’s OK, I’m not going to touch her,” Burnside said to the principal, only moments before walking over to the teenager.

She pulled the teenager down by her hair for about 20 seconds, leading to the girl screaming in pain.