A 13-year-old was robbed at knifepoint outside a Uniondale school, police say.

It happened on the soccer field of Turtle Hook Middle School on Jerusalem Avenue Thursday at 2 p.m., police say.

The suspect, who has not been identified, allegedly went up to the teenager, flashed a knife and then forcibly removed the victim's sweatshirt.

Detectives say the suspect is charged with robbery, menacing and criminal possession of a weapon on school grounds.