“Are they engaged in the content after the game is over, two days later, or at some point in time when they are not having all the bells and whistles going off?” asked Heather Collins, a digital learning researcher and chairwoman of the behavioral and social sciences department at Trident Technical College in Charleston, S.C.  Kahoot, a play on “in cahoots,” capitalizes on a number of education trends. One is “engagement,” or the belief that the more an activity interests students, the more motivated they will be to learn. Another is “gamification,” the practice of applying elements from games to nongame realms.  “It is a simple game-show format,” Johan Brand, the chief executive of Kahoot, said in a phone interview.  The spoonful-of-sugar approach to learning can be applied regardless of subject matter. “We as a company are not interested in what they are teaching,” he said. “We are interested in how they are playing.”  And many students are playing to win, partly by competing on speed.  “They think the cellphone is faster,” Ms. McGaughy, the digital learning specialist, said. “So the competitive kids use the phone.”  The site also lends itself to social sharing. Students are already posting their Kahoot ranking on social networks — or group-texting it, even when they do not come in first.  Here is a student posting on Twitter as @beansalaad: “I finished 5th in the @GetKahoot quiz ‘How does the Constitution protect freedom of expression’ out of 22 players, with 4,754 points!”  But the constant competition and quantification could also be off-putting.  “Some people love being ranked and having points and status,” says Neil Selwyn, a professor of education at Monash University in Melbourne, Australia, who studies how schools use technology. “But I bet it doesn’t appeal to every student in the same way.”  Mr. Brand, a digital marketing and experience designer, founded Kahoot with two colleagues in 2012. It has since raised about $6.5 million from its own employees, from the Research Council of Norway and from Northzone, a venture capital firm that was one of the first investors in Spotify, the streaming music service. The founders focused first on the American school market, introducing the product in 2013.  Mr. Brand previously developed games services for companies like Daimler and Unilever. He also worked on a marketing project to help family-run inns, scattered throughout the Norwegian fjords, become more collaborative — by talking up their fellow inn owners to guests rather than competing with one another on hotel amenities. Guests found the owners’ stories so compelling, Mr. Brand said, that they grew more interested in visiting other fjord hotels.  Mr. Brand’s expertise in identifying stimuli that can trigger powerful emotions came in handy as the co-founders were working on Kahoot. He said that some of his thinking was also inspired by a book titled “Hooked: How to Build Habit-Forming Products.”  “We are using music, timers and points, these emotional triggers,” Mr. Brand said. “We are not just designing for the logical sense,” but creating “for the emotional side — where you fall in love with what is going on.”  The brand’s novel social-learning story notwithstanding, Kahoot seems like a bit of a throwback to a more old-fashioned pedagogical approach: behaviorism. This is the idea of educators shaping student behavior by handing out gold stars, stickers, points and the like.  Readers who attended school in the pre-laptop era may have played classroom games like multiplication bingo, an offline exercise in which students win acclaim or prizes for being the quickest to remember their times tables. Today, students may use Ascend Math, a learning app that rewards students who complete a level by letting them play short video games.  Of course, points, bells, video game leaderboards and all sorts of other brain stimuli can become habit-forming — like ice cream. That does not make them good for students.  “If you get an ice cream sundae every day after dinner, you are going to expect that ice cream sundae every day after dinner,” Professor Collins, the learning researcher, said of Kahoot.  Mr. Brand said Kahoot was not intended for teachers to use with their classes every day, but once or twice weekly.  “Life cannot just be a Kahoot,” Mr. Brand joked. “Actually, that would be very boring.” More seriously, Mr. Brand said: “From the outside, Kahoot may look frivolous. But if you are a teacher, you can see students are emotionally engaged in the material.”  He added that the start-up was more focused on looking at how the quiz system affected students’ interest in attending school and learning, rather than their academic performances. A small study by the start-up of college students in Norway concluded that there was no significant difference in test results between those who took a Kahoot quiz and those who took a traditional quiz on paper. But the Kahooters reported enjoying their experience more.  “We are looking at emotional engagement,” Mr. Brand said.  Kahoot is free for educators, who can upload their own questionnaires or choose among several million quizzes that other users have posted. The company has begun to generate revenue by charging publishers to include quizzes with their material on the site. It also offers a fee-based service for companies to use Kahoot for consumer marketing or to engage employees in corporate information.  Many educators run Kahoot to get a quick snapshot of how their class is doing.  “They can get immediate feedback on how many students answered correctly and which questions students are still struggling with,” said Susan Rieke-Smith, the superintendent of Springfield Public Schools in Springfield, Ore. “Then they adjust the lesson plans for the next day based on that data.”  Some teachers also use Kahoot to introduce a lesson, as a way of piquing students’ interest in absorbing unfamiliar material.  Nolan Sullivan, a social studies teacher at La Salle Academy, a Catholic high school for boys in Manhattan, prefers to use Kahoot without the video game music or the gong. He says he often asks his ninth graders to devise their own questions on subjects they learn in class, such as medieval or Islamic history. Then he incorporates them into the quiz.  Asking his students to create their own questions, he says, gives them extra motivation to understand their lessons. It also has them coming back for more.  “When we are doing test prep, my students will say, ‘Mr. Sullivan, are we Kahooting tomorrow?’” he told me. “Kahooting is an actual word now.”  A version of this article appears in print on April 17, 2016, on page BU3 of the New York edition with the headline: Pop Quiz? Now It’s All About the Quiz App. Order Reprints| Today's Paper|Subscribe
The learning game, made by a Norwegian start-up, is sweeping American schools. Over a third of elementary and secondary students used it last month.