The item was reportedly found at Elms Elementary in Jackson.
EMS and the fire department set up a staging area at nearby Geotz Middle School, where students were relocated.
Officers and detectives conducted interviews of the student and the student's parents, who indicated that the item was an inert practice grenade that had been purchased at a flea market.
The incident remains under investigation pending an examination of the grenade by the New Jersey State Police Bomb Unit, to confirm that the grenade is not live.
The school released the following statement:
"Students in the Extended School Year/Camp P.A.W.S. program at Elms Elementary School are now being brought back to Elms after being relocated temporarily to Goetz Middle School this morning while police investigate the presence of a suspicious item brought to the school this morning in a student's backpack. The backpack remained in the parking lot outside the building while police investigated.
Students who arrived for the 8 a.m. program at Elms were brought across the street to the Goetz Middle School by district staff and district buses. Students who were scheduled to arrive for the 9 a.m. program were dropped off directly at Goetz Middle School. All school staff at Elms were also moved to Goetz.
There was no cause for alarm. The students were not in harm's way. Students remained with their district staff members at Goetz until police informed us they could return to Elms at 10:30 a.m."