The mother of a boy killed in the Joplin tornado nearly five years ago says she's upset the school district won't leave an empty chair in honor of her late son during the next commencement.

Tammy Niederhelman says Zachary Williams was 12 when he died in the 2011 tornado that killed 160 other people. Williams would be part of this year's graduation class.

Niederhelman tells the Springfield News-Leader she asked Joplin school administrators to include during the next commencement ceremony an empty chair on which Williams' cap and gown can hang. And that his name is called.

Niederhelman says school officials told her it's against policy to allow the empty chair at graduation.

A message seeking comment was left Friday with the Joplin school system's interim superintendent, Norm Ridder.

Joplin, Missouri Reels After F5 Tornado Devastates Town, Kills 125
Joe Raedle, Getty Images