"Viral adoption"（病毒采纳） seems to be part of just about every edtech business plan we at EdSurge have had the privilege to hear this year. That raises two questions: what does "viralness" mean for edsurgents? And which edtech company has the most viral mojo（巫术；符咒） right now?

"Viralness" seems to last about as long as a firefly--or worse, an "Old Spice" commercial. (Flashback: July 2010. Old Spice racks up 23 million views in 36 hours for video ad campaign. Total duration of the campaign: three days. Is there something odd about having a quickie stick-deodorant campaign?

Edtech’ers don’t need that kind of burst--instead, they need fast growth among users who will, um, stick.

The Khan Academy is usually the site most consider viral edtech. Its stats: Academy reported 3.5 million unique users per month as of October 2011, which is up 309%, year-over-year.

But there are other big players, including some who are seeing new growth spurts.ePals, which launched as a for-profit site in 2006, had 6 million users (including students and teachers) earlier this year and has been aiming for 10 million by year-end. (Earnings--and numbers--are due out at the end of November.) Fresh work overseas (such as in ePals China and ePals Europe) is catalyzing growth.

ePals executives also say that large districts or groups putting heavy emphasis on security, policy management and "instructional value that scaffolds learning."
Flashcard and homework help site Quizlet, launched in January 2007, has 6 million unique visitors a month and has seen 32 million unique visitors over the last 12 months. Advice from COO Dave Margulius: "Make it free and really easy to sign up and use. Appeal to two mutually reinforcing segments (such as students and teachers)."

EverFi, which offers online financial literacy and alcohol awareness programs and launched in 2008, reports 4 million students have completed its programs, up from 3 million earlier this year.  Its network includes 46 of the 100 largest school districts and big buck support from foundations and investors.

And then there’s teacher-driven social networking (and homework) site Edmodo, which hit 4 million users as of late October.  Viral signs: Labor Day 2010, Edmodo had 500,000 users; a year later, Edmodo hit 3 million. "The key driver tends to be the word of mouth from other teachers," says Betsy Whalen, vice president of community. What they tell her they like: "They feel Edmodo keeps kids safe and protected and they feel like we listen to them," she says. "Every new feature we release can be tracked directly back to a teacher request. "

We caught a glimpse (sorry, our spy camera broke down) at some numbers from startup ClassDojo, that had a touch of viralness. ClassDojo is a free tool teachers can use to reward positive classroom behavior. CEO Sam Chaudhary is shy about sharing numbers, offering only that "thousands of teachers in 20 countries" are using it since its launch in September. Of course, ClassDojo got a nice boost by winning NBC’s Education Nation innovation challenge (also in September).

Words of advice from Chaudhary: "Make sure you solve a problem for a specific, addressable group of users: before we coded anything, we started by trying to really understand the problems we could solve. We interviewed over 100 teachers on what their biggest pain points were to get a deep understanding of the space."
 
Common to all those we spoke with: hyper-responsiveness to users. Says Chaudhary: "We try to get back to all emails from users within a day (or two). Listening to any users, but in particular teachers (who don’t get the attention they deserve from software-makers!), is a great form of building engagement."