In an era of ubiquitous i­Phones, Varsha Gunda is playing an analog riff on the game of telephone.

She is staring at a model on a table in a brick school building in Washington. She gets up again and again to get a better look, scrawling every detail on three-holed paper. No pictures allowed. Her hand is getting so tired she has to keep shaking it.

Varsha, a sixth-grader from Ashburn, Va., was one of 900 middle and high school students who spent Saturday at the National Cathedral School for an early season warm-up in the national Science Olympiad competition. In 2016, 24 teams showed up for a similar meet at the school. This year, 63 teams from across the region made it, facing a gantlet of 23 events covering topics as diverse as food chemistry and fossils. Walter Johnson High School in Montgomery and Longfellow Middle School in Fairfax came away victorious.

In room 316 Saturday morning, Varsha and a dozen competitors were in the first stage of the “Write It Do It” challenge. It was nearly silent but for the hum of the heater and pencil scratching. They had 25 minutes to jot down every detail of the makeshift sculpture before them. Then each of their teammates in another room on another floor would have to rebuild the sculptures using just those written notes.

It was a bit like a deconstructed episode of “Chopped” or “The Great British Baking Show,” with the contestants racing the clock to write down long ingredient lists and meticulous recipes for how everything should all come together.

Chris Semonsen, an environmental lawyer from McLean who was supervising the challenge, said the intricate structures were designed to make them tricky to describe, and they were reliant on precise and efficient instructions to reproduce. “That’s what engineering is all about,” he said.

Given the tendency for people to talk past each other, it was also a reminder of how important it is to communicate clearly, even if only about an upside-down disposable plate with a foam cup placed just so. Or about a pair of skewers jutting out like clock hands striking 10. Or strategically placed pink, blue and orange Post-it Notes.

“Stop!”

Time was up for the Writers, and parents carried the instruction sheets to the Builders waiting downstairs, including Varsha’s partner, fellow 11-year-old and sixth-grader Veera Anand. They both attend the private Nysmith School in Herndon.

Veera and the others took the parts for the makeshift sculptures from zip-top bags and started to read, interpret and remake the sculptures, this time with added time pressure. The tiebreaker for teams that built similarly successful copies was who got it done first. Pressure built when one student announced he was finished after just 10 minutes.

It was not all smooth.

“Do you know if my writer didn’t get the maximum amount of time?” the quickest finisher asked as the students streamed out to their next challenge. Indeed, his teammate had arrived 10 minutes late to the writing half of the challenge, leaving the instructions unfinished. Another builder noted that his partner was colorblind and had described the precise placement of three yellow Post-it Notes, though there were none.

Varsha and Veera had practiced together, and “we realized he’s the better builder and I’m the better writer,” Varsha said.

“I decided to flip my perspective in a way where he could realize it, where he could visualize it,” she said.

“Understand it,” Veera added.

“I wanted to explain it in a way that wouldn’t be too simple and wouldn’t be overly complicated,” Varsha said. She even described the “olden-days laundry pins” that were part of the structure, because she wasn’t sure he’d know what they were.

They did have their challenges.

Varsha had originally referred to left and right in her instructions, but scratched that and changed it to north, south, east and west. She instructed Veera to place the Post-it Notes on the north side of the disposable plate. But they got their signals crossed on which side was north, and he went the opposite way.

His lesson, he joked afterward: “Everything Varsha says, do it flipped.”

Elsewhere, Semonsen’s daughter, Serenna, who attends Longfellow, which is in the Falls Church area, was competing against the boys in the “Ping-Pong Parachute” competition. It involved air-pressure powered bottle rockets blasting into the rafters at the gym. Whichever team’s ball took the longest to float down from the soaring rocket would win.

“Even though its pretty stressful,” the competition had the feel of a “big family,” said Serenna, 13, with a chance to team up with people you might not otherwise have an opportunity to connect with.

“This event is a lot of trial and error with different parachute sizes,” said fellow Longfellow student Jaiden Khemani, 13. “If you make it too small, it will just fall to the ground. But if it’s too big, it will be too heavy. Then it just falls. It’s about finding a perfect balance.”