A 12-year-old was arrested at his Dorchester elementary school Monday morning after the school’s staff found an unloaded firearm and another weapon in his bag, school officials said.

Staff at the William Monroe Trotter school, which serves students in kindergarten through eighth grade, were conducting an “administrative search’’ of student lockers around 8:23 a.m. when they found the weapons, said Boston police spokeswoman Myeshia Henderson. The student was arrested for being a delinquent and for unlawful possession of a firearm on school property, Henderson said.

Principal Mairead Nolan said in a statement that police were “immediately called’’ after the discovery. Nolan added that in addition to police action, the student will also be disciplined according to the Boston Public Schools’ code.

“I want to ensure you that the safety of our students and staff is always a top priority at BPS,’’ Nolan said. “We followed all the appropriate steps to ensure that no one in our school community was in any danger.’’

No other information was immediately available from police or school officials.

Samantha Gross can be reached at samantha.gross@globe.com.