Three steps to starting college: Meet roommate. Unpack in dorm room. Then, sometime during orientation, hear music, see a student start dancing, watch as more dancers join in, and join the campus flash mob. (Or if you miss the actual event, watch it over and over on YouTube, to see how many people you recognize.)

Outbursts of seemingly impromptu dance numbers were so common at orientations this year that BostInnovation, a Web start-up chronicling Boston life, ran a contest asking readers to watch the YouTube videos and vote for the local campus — Wellesley, Merrimack or Emerson — with the best welcome. (Wellesley won.) There was even a flash mob to greet new students at a medical school, the University of Alabama at Birmingham.

The college-sponsored performances, which have grown to feature coordinated costumes and appearances by tweedy officials, sometimes suggest the dance equivalent of the school fight song, a far cry from the roots of the genre — informal gatherings hastily called via social media.

Nonetheless, their popularity is growing.

"There’s definitely a cool factor to flash mobs," said Kevin Kruger, associate executive director of Naspa, a national association of student-affairs administrators. "It’s something students will talk about, and it can help colleges brand and market themselves. It’s a way to hook students, and build community and pride in place. It gets new students superconnected, right from the start, which is one of the goals of orientation. For students, I think part of the appeal is that it goes on YouTube, and you get to watch yourself, which is a kind of self-promotion this generation likes."

While flash mobs have been known to have a darker side — in Philadelphia, the police imposed a curfew after a violent confrontation — on campus, it is all about dancing. And not just at orientation. Last week at UCLA, there was a flash mob wedding proposal, in which the whole crowd dropped to its knees for the ask.

Fraternities and sororities have sponsored them, as have residence halls. And they are becoming de rigueur for celebrating new programs, or big anniversaries: Portland State University had one last month at the opening of Electric Avenue, a street dedicated to electric vehicles, as did MIT’s 150th anniversary celebration and the University of Minnesota School of Mining’s 75th anniversary.

The large official events may lack the somewhat spontaneous, almost surreptitious feel that originally characterized the genre. The Minnesota mob, for example wears gold and maroon T-shirts, and is joined by both Goldy Gopher, the school mascot, and Steven Crouch, its dean. At California State University San Marcos, orientation leaders wearing blue "I (Heart) CSUSM" T-shirts are joined by not only the mascot but a campus police officer as well.

Mascots, like the Rose-Hulman Institute of Technology’s adorable little elephant, or the University of Mary Washington’s large dancing eagle, were much in evidence at orientation flash mobs.

But more modest midyear efforts, like a lunchtime dance at Bowdoin College, remain true to form.

The campus performances get enough attention that GoEnnounce.com, a online graduation-announcement business, used them as an advertising vehicle, sponsoring student-produced flash mobs where the dancers (at the University of Michigan, wearing caps and gowns) finish by holding up large cards spelling out G-O-E-N-N-O-U-N-C-E.

While college flash mobs vary enormously — students at the College of Charleston held a yoga flash mob — most start with one or two dancers, and a group of quietly bewildered onlookers, who laugh, cheer and pull out their cellphones to record the whole thing, as more dancers arrive. The initial participants are usually good dancers, but those who join in tend to be more awkward, occasionally leaning the wrong way, or flailing their hands a bit behind the beat.

For orientation planners, it adds up to a cheap tool for boosting school spirit. "We thought it would engage a lot of people from different parts of the college, and send a nice message about what it is to be part of the Wellesley community," said Lori Tenser, dean of the first-year class at Wellesley. "I knew it was going to be good after a long rehearsal, when one of the students said, ‘If I were a first-year, and I saw this on my second day, I would be so happy, and feel I’d come to the right place."’

The Wellesley group, using Katy Perry’s "Firework" — probably the flash-mob top pick this year, along with Taio Cruz’s "Dynamite" — rehearsed for six hours during the student leaders’ training week, and posted the moves on YouTube for those who needed more practice.

Buffalo State College went further, putting a short instructional video teaching the Wobble, a line dance that was a central feature of the flash mob, on its Facebook page for the 3,000 incoming students.

"We wanted to pull in as many people as possible," said Daigi-Ann Thompson, a theater major who taught the dance on video. "The Facebook page got the freshmen all excited. All they knew was that at some point in orientation, they’d be asked to do it."Robert Mead-Colgrove, SUNY-Buffalo’s orientation director, said he spent less than $100 on the whole project, the only costs being sound equipment and a DJ. Thompson and others worked on the choreography all summer, and held hours of rehearsals, official and unofficial, in the days leading up to orientation, with residence advisers, orientation leaders, office assistants and administrators all trying to learn the dance.

"They rolled up their sleeves and loosened their ties, and I had the vice president of student affairs doing the Wobble right next to me," Thompson said. "It was a big success. We’ve been asked to perform it again, at a couple other things, so we’re rounding up more students."

But while many institutions have a college song, sung year after year, the prospect that a flash mob could become the college dance, or even a regular part of the orientation schedule, raises a metaphysical question, one that is already plaguing some orientation directors: Without the element of surprise, they wonder, would the spirit of the flash mob be destroyed?