By listening to its core audience--teachers--ClassDojo's educational software has reached 90% of U.S. schools. Now the real work begins: how to get someone to pay for it.

Sam Chaudhary and Liam Don, two education technology entrepreneurs with experience as teachers, launched ClassDojo in 2011 and have seen it grow to reach more than one million users.

"Four out of 10 teachers say they spend more of their time in class managing behaviour than teaching, time which they want to dedicate to the classroom. "ClassDojo offers them a solution.