A stray bullet shattered a school window and hit a chalkboard inside a packed Brooklyn classroom Tuesday, police say.

It happened at South Shore High School, located across the street from the Glenwood Houses on Glenwood Avenue in Canarsie, just after 11:30 a.m.

Police say a group of men got into an argument outside the housing complex and then began firing shots.

One of the bullets went through a fourth-floor classroom window and became lodged in a blackboard. At least 17 students were inside the classroom at the time, but none were injured. Students say they were placed on lockdown for two class periods after the incident.

The Department of Education says it will continue to work closely with the NYPD to ensure the safety of the school building.