Many students at one California school district were unable to take part Wednesday in a nationwide protest against gun violence after one of them threatened to shoot classmates.

All schools in the Atascadero Unified School District were locked down after the threat, and a planned walkout protest was canceled after students were asked to shelter in place, reported The Tribune.

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Police learned just before 8 a.m. that a student threatened to shoot up Atascadero High School, and officers went to the teen’s home about 8:10 a.m.

The teen was taken into custody and booked into the San Luis Obispo Juvenile Services Center, police said.

Police said the boy acted alone, and officers did not find any guns at his home.

Some high school students walked out to take part in National Walkout Day, which was planned on the one-month anniversary of a deadly school shooting in Parkland, Florida.

No additional information was released about the threat to Atascadero schools, which remains under investigation.