Police were called to the Diagonal Road school at Glenelg East at 10am on Tuesday August 9 after the reported assault.

The student reported that the man approached her on the first floor of the main building, grabbed her wrist and pulled her down the stairs onto a middle landing.

She told police she was able to pull away and he ran down the stairs and left the school.

He is described as being about 180cm tall, bald and wearing a knee-length light blue coloured shirt, black pants, black disposable face mask and carrying a black beanie.

Police said the student also reported that the man wore purple nail polish on one thumb, as well as a distinctive black ring with bright dots. He also wore a black twisted bracelet on one wrist and had four earrings in one ear.

Police said detectives had spoken to students, staff and parents who were around the time, conducted extensive door knocks and viewed  CCTV footage from the area but were yet to find any witnesses to the incident.

Anyone who recognised the man or has any information that may lead to his identity is asked to contact Crime Stoppers on 1800 333 000.