A gun was found in a backpack Thursday afternoon at Olathe Northwest High School.
Students at the school and a nearby middle school were held in classrooms past their normal dismissal time while police and school officials looked for the person who owned the backpack.
They were given the all clear and allowed to leave about 4 p.m.
The school is located at College Boulevard and Lone Elm Road. Students at nearby Prairie Trail Middle School were also held in their classrooms as a precaution until the all clear was given.