He said the investigation and search for a possible weapon are ongoing.
According to authorities, a student alerted a school staff member that another student at school had a gun. The staff had not seen a weapon.
The streets surrounding the school, Clinton Road and Henderson Drive, were shut down during the search for a weapon. But West Caldwell police said the investigation was contained to the school, and did not affect other schools or area businesses.
Essex Valley School is a "therapeutic alternative" school which takes in students that have struggled in other more traditional schools, according to its website. The school offers both vocational services and counseling, and expanded its roster of counselors in February, according to a school newsletter.