Schools across the U.S. are upping security after a TikTok “challenge” promising a wave of school shootings, despite authorities deeming the threats “not credible.” The online dare dubs Dec. 17 “American School Shooting Day.” Other details are murky, and how many students ever planned to participate is unclear, but many schools are on high alert. A Houston district ordered all students to leave their backpacks at home Friday. Panicking parents are flooding their kids’ schools with calls. One Florida district tweeted, “Many of our schools are being inundated with parent calls this morning asking about these latest threats and their validity.” Multiple school districts have increased the number of police officers on their campuses. By contrast, Baltimore County Schools tweeted, “Law enforcement agencies have investigated this threat and determined that it originated in Arizona and is not credible.”

TikTok itself issued a statement on the matter Thursday: “We handle even rumored threats with utmost seriousness, which is why we’re working with law enforcement to look into warnings about potential violence at schools even though we have not found evidence of such threats originating or spreading via TikTok.”