The episode played Thursday night and had the kids at fictional McKinley High locked in their choir room after hearing shots inside the school.
The students turn out the lights, cry, and send text messages to their family as they wait to see what happens next.
After a few moments it’s discovered that the character Becky, a Downs syndrome girl had brought the gun to school and fired it accidently without hurting anyone.
The episode has drawn a huge amount of criticism from Newtown, Connecticut, where the killings happened at Sandy Hook Elementary school took place in December.
Writing in the Newtown Bee Shannon Hicks said the show "may be a little much for some residents to stomach."
Some residents of Newtown are upset the episode was aired and others are mad they weren’t warned ahead of time by the network.
One said "I think it’s terrible that the writers and producers of that show didn’t think to contact someone in Newtown to let us know this was coming."