Trumbull Police announced the arrest Sunday, a day after he made the posting.
They say a parent of one of the other students alerted them to the post after they saw it on their child’s cell phone.
Police say they determined there was no threat to the public. They say it turns out he was holding a BB gun and had cropped out the gun’s red tip when he took the picture.
The boy, who was not identified by police, was charged with disorderly conduct and was scheduled to appear in court March 3.