At Fairmont Junior High, students noticed a fellow classmate with a gun around 2:30 p.m. and reported it to a teacher, school officials said. After the teacher called the front office, the school resource officer, along with Pasadena police officers, came to take the student into custody.
It wasn't immediately clear how the student got the gun or why they brought it to school.
Investigators have yet to release the identity of the student.
Fairmont Junior High, located on Holly Bay Court, is home to about 825 students grades 6, 7 and 8.
RELATED: HISD changes story on gun charges tied to on-campus incidents