DARBY, Pa. (WPVI) -- Action News has learned a Penn Wood Middle School student has been arrested after police received a tip that a student had a gun in their locker.Darby Borough Police Chief Robert Smythe says police were out on another call Thursday when a student tipped them off to the gun.Officers tracked down the student and the .40 caliber semi-automatic handgun, and the student was taken into custody.Additional police presence was at the school, located in the 100 block of Summit Street, during dismissal to ensure the students' safety.Smythe says police have been called to the school several times this week for numerous reports of disturbances.There was a fight there Wednesday, police say, and tension has been building.School officials sent a letter home to parents stating, "At no time was the handgun visible or used to threaten students."