After the device was confiscated, the administrative offices were evacuated, and the entire school was locked down.
Police said the device was equivalent to one-third of a stick of dynamite. It was detonated without causing injuries.
Authorities and school officials say the student had no intentions of causing harm.
The boy was taken into custody. He also was suspended from school for 10 days, pending a hearing that will determine whether he will be expelled for a full calendar year.
(Copyright 2009 by The Associated Press. All Rights Reserved.)