Teens 'street planking' in San Jose, Calif.

Looking at a picture of his buddy stretched out, face down, atop a stove like a really big fish about to get fried, Daniel Geraghty didn’t get it.

“I was so confused,” says the junior at Clarksville’s River Hill High. “I was like, ‘What are you doing? Why are you sending this to me?'”

Then two days later, there he was himself, lying nose-to-tile on the stairway in school between classes as kids stepped around him, staring and laughing.

“I’m a newfound planker,” he declares. “It’s the hugest thing right now.”

Just like that, another devotee for “planking”—a head-scratcher of a global craze in which people lie stick-straight like a plank, snap a picture of the pose, and then post the shot online.

Jaw-droppingly silly yet ragingly popular, the trend—fueled by the notoriety the internet can provide—has infiltrated shopping centers, bars, beaches, and schools … to the chagrin of educators tasked with keeping students safe and well behaved.

Tom Evans, principal of Eastern Technical High School, a magnet school in Baltimore, can only shake his head. That and get on the PA system last week and warn kids that planking was not a school-endorsed endeavor. By then he’d already seen pictures of his students planking across a cluster of classroom desks, over lavatories, and draped atop a candy machine.

“I told them they don’t have to be permission to climb on top of anything in this building,” Evans said. “It’s just goofy behavior, but I don’t want anyone getting hurt or doing something stupid.”

In recent days, when Geraghty hasn’t been stretched over the roof of a sedan, splayed across the top of a coat rack, or lying along a narrow brick ledge, he’s been crowing about his exploits on Twitter.