A man was spotted carrying a .22 caliber gun on a sidewalk near Groton Elementary School around 10:15 a.m.
Groton School Superintendent Jim Abrams says a custodian spotted the man and alerted the principal, who contacted police and initiated a lockdown procedure.
Abrams says the children were kept in the building and continued the day normally as possible.
He says the doors to the school are always locked.
Abrams says police have not been able to locate the man, but says they know who he is.
An automated call was placed to parents at 2:00 p.m., when the man had not been located. The school dismissed as its usual time of 3:00 p.m. with a modified release. Children were not to walk home and students who did not take the bus were picked up.
All afterschool activities in the district are canceled for Tuesday.
Abrams says school officials are staying in contact with police in case the man is located.
The status for school tomorrow has not yet been decided.