The investigation began around 12:10 p.m., when officers were called to investigate a student "acting suspiciously" at a school in Perth Amboy, local police said.
The student was believed to have been headed toward another school looking for another student, police said. The student was taken into custody and was found to not have been armed, police said.
The shelter in place was lifted later in the day. The investigation is ongoing.
Click here to follow Daily Voice Hamilton Township and receive free news updates.