As she enters her third year of teaching third grade, Dianne Rhodes--better known to her students as Mrs. Rhodes--is also heading into her third year of using ClassDojo, a little app on her phone that has changed the way her classes are taught and how she communicates with parents.

"The parents really seem to like when I post pictures of what's happening, especially during our first few days of school or if we're doing an art project," said Rhodes, who teaches at Bel Aire School in Tiburon, California. "It's fun to get those notifications to see that they're watching what's going on in the classroom."

Since its launch in June 2011, ClassDojo has rapidly diffused throughout classrooms across the U.S. and around the world. Along with paper, pencils and whiteboards, the app is among the few pieces of technology that have become ubiquitous in K-8 classrooms. In the U.S., more than two-thirds of all schools have at least one teacher who is active on the service.

"If we can shift what happens inside and around classrooms then you can change education at a huge scale," said ClassDojo CEO and co-founder Sam Chaudhary. ClassDojo was one of Inc.'s 2015 30 Under 30.

The app first came to fame for a point system that let teachers reward students for good behavior, similar to giving out gold star stickers. At the time, the app drew criticism from privacy pundits, but since then, ClassDojo has evolved into much more--a service that lets teachers and parents remain in constant communication around what their student is learning every day.

"They can see the positive feedback that their kids are getting," said Rhodes, who estimates that at least a third of the teachers at her school use the app. "Normally you're not going to call every single parent every single day and say, 'Oh your child was a great listener today.'"

Aesthetically, the app looks like a dark lavender Facebook, with teachers posting photos about their lessons and parents able to like and comment. Prior to this school year, ClassDojo borrowed a feature from Snapchat and introduced Student Stories, which let students post photos and videos about their day at school.

But in terms of its purpose and the way users adopt the service, Slack would be ClassDojo's closest comparison. When it comes to Slack, it's the end users who choose the service, going around the company's IT officials and downloading it on their own. Similarly with ClassDojo, teachers can download the app by themselves, without having to ask school administrators for permission or money to pay for the software.

For Slack, keeping coworkers connected throughout the day is the objective while ClassDojo is meant to do the same for the support system of every student, keeping teachers, parents and school administrators on the same page. The purpose is to ensure that parents are as involved with their students' work every day as they are during their annual parent-teacher conferences.

"At the end of the day when I pick [up my son], I can just be like 'Hey, how did this go in class?' instead of him saying 'Well, I didn't do anything in class today,'" said Hilary Morrison of National City, California. "You don't have to be playing the guessing game when they get out of school."

Having connected parents and teachers, five-year-old ClassDojo is now beginning to turn its attention to the next part of its journey: monetizing the service. The company said it has no plans to sell advertising. Instead, ClassDojo is looking at selling educational content. With access to so many teachers and students, the startup is leveraging its distribution capabilities to spread educational videos to an audience of teachers and students on a level that's never been seen before.

"Schools are paying hundreds of thousands of dollars for curriculum and software that's delivered in boxes," said Liam Don, ClassDojo co-founder and chief technology officer. "With the kind of reach that we've got here and if we can really power every classroom in that kind of scale, we can eliminate so much of that cost."

ClassDojo began toying with this idea in January by teaming up with Stanford University to produce and release a series of videos around the educational theory of the growth mindset. The videos were seen by an audience of 15 million students, which is approximately one out of every four K-8 student in the U.S., ClassDojo said.

ClassDojo will build on this success by releasing its second set of videos, this time produced in partnership with Harvard University with a focus on empathy. For ClassDojo, the goal is to begin releasing this type of content on a regular basis, ideally once a week.

Content like Stanford's growth mindset videos will be available to all users, but the idea is to make available enough content that parents and teachers will be willing to pay extra to give their students access to more than the basics and continue learning beyond the classroom.

"It's a huge distribution platform to reach parents," Don said. "We want to, In the long term, enable parents to be consumers for their child's education."

If this sounds familiar that's because it's essentially the same freemium model used by Slack (among other enterprise-software services). All users are given the basic tools to benefit and enjoy the service, but for those willing to pay extra, more is added to enhance the experience.

"Your entertainment bundle is Netflix. Your music bundle is Spotify. What's your education bundle?" Chaudhary said. "It's not clear that exists today."

ClassDojo can see its route to monetization clearly enough, but the company is being careful not to rush into the process. The focus remains on growing its user base and improving the product, and for now, Chaudhary and Don are enjoying the patience of their investors.

"This company has a greater market share than Coke in the U.S.," said Hemant Taneja, a ClassDojo board member and managing director at General Catalyst, which led the company's $21 million series B round in April. "Let's get all the stakeholders on the platform. Let's get them on and scale before we think about monetization."

There's no rush from investors, but ClassDojo users are eager for more content. Some have even said that there's no question they'd be willing to pay.

"Just knowing the content that they've put out, how well it's been done and how much of an impact this has made in my classroom, I would buy it hands down," said Stephanie Smith, a fourth grade teacher at Roy Waldron Elementary School in LaVergne, Tennessee. Although it may be a while before ClassDojo begins selling this content, Smith said she already considers the app to be much more than just a classroom management tool.

"It brings everybody who is in that child's life together," she said.