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GRASS VALLEY, Calif. (KTXL) — A mask worn by an eighth-grader is at the center of an incident that occurred at a Grass Valley middle school. 

The mother of the Lyman Gilmore Middle School student said she is disappointed and hopes it is a one-time incident. 

“That is not the American flag. That is the new Confederacy flag,” said a substitute teacher. 

It was a thin blue line mask worn by Lucas Lillar. A video recorded by another student shows him arguing with a substitute teacher. 

Watch the video by clicking or tapping here.

“I was confused at that time because I didn’t know what he was talking about,” Lucas said. 

Lucas said he was working at his desk when the substitute approached him over his face mask. 

Supporters of the thin blue line say it’s their way of supporting law enforcement. Lucas said he wears it to support his father, who is a police officer. 

“I was angry because these types of things should never be in the classroom,” said Amanda McCallum, Lucas’ mother. 

McCallum said she was shocked to hear about the argument. She told FOX40 her son had the same teacher last week and wore the same mask, but there was no issue. 

“These topics need to be left at the door. The school is meant to educate our children in a safe environment and I don’t feel like this was a safe environment, but it needs to be. We are entrusting these people of authority, these teachers with our children,” McCallum said. “We are in a time where we are so divided that we need to learn to be kind and respect each other.”

McCallum hopes to meet with the superintendent next week. She said she met with the principal and was told the substitute teacher will not be working there again.