Police were called to Glenelg Primary School yesterday at about 10am after reports the man allegedly grabbed a girl on the arm and then fled the area.
It is believed he broke into the school and walked through the grounds, into the school building, up two sets of stairs and outside a toilet block.
The man allegedly grabbed the girl on the arm before he left the area.
Parents from the school told 9News they had been sent a text from education officials about the incident.
“It’s pretty scary… It is a massive concern that anybody from the outside can walk in and get the kids,” one parent said.
Police described the man as being about 180cm tall, bald and was wearing a knee-length light blue shirt, black pants, black face mask and carrying a beanie.
Officers have spoken with students, staff and parents who were at school at the time of the incident, but are yet to identify any witnesses.
Anyone with information should contact Crime Stoppers on 1800 333 000.