Police say the incident happened at Portage Trail Community Junior School, located at 100 Sidney Belsey Cres. in the area of Jane Street and Weston Road.
At about 2 p.m. a student walked into the girls washroom and was approached by a man, who police say grabbed her, causing her to fall.
The girl was able to get to her feet and ran from the washroom and into a nearby classroom, where she reported the incident.
The suspect is described as white, approximately 30 years old, tall with a skinny build, full beard and thick moustache.
Police are reviewing footage from the school's security cameras.
He was wearing a black toque, black sweater, black shoes with blue stitching, and carrying a black satchel.