What do personal computers, cell phones, and digital cameras have in common? They all started on the fringes. Then they hit a tipping point and, suddenly, they were everywhere.

This past year, I believe “open curriculum” — or curriculum that is free and adaptable — hit a similar tipping point in K-12 education. For the first time, more school districts chose an open curriculum over work developed by traditional publishers, like Pearson.

This is a welcome change. Using open curriculum (also referred to as Open Educational Resources, or OER) saves a district money. When districts choose a free curriculum they spend on printing and/or a web-based platform for hosting and managing digital curriculum. That’s a lot less than the millions they spend on traditional textbooks. In fact, it can cut costs by as much as $50 per student.

For years, districts have worried that the dollar savings are erased when you consider the hard work to piece together curricula from scratch. Not anymore. Now, for the first time, they can access complete open curricula. The EngageNY curriculum, for instance, provides teachers with everything they need to teach math and English in Kindergarten through 12th grade.

The EngageNY K-8 math curriculum was also the only one to receive a top rating by EdReports, a curriculum reviewer. Even Go Math, Houghton Mifflin Harcourt’s top elementary math curriculum, received a rating of “Does Not Meet Expectations” because it was not appropriately aligned to the new standards.

But this is only the beginning. Open curriculum will continue to eat traditional curriculum. There are four reasons why:

The transition to digital is accelerating

The more schools go digital, the more open curriculum becomes a viable option. That’s because teachers access open curriculum over the Internet. And schools are about to gain much greater access to high speed broadband.

In the next five years, the Federal E-Rate program will spend over $8 billion to ensure that 99% of students have online access. Combine that with the dropping cost of hardware, and you have fertile ground for conversion to open curriculum.

The number of full, open curriculum options is growing

EngageNY provides one option for open curriculum — but more are on the horizon.

The K-12 OER Collaborative, an initiative supported by eleven states and a host of organizations, including the Council of Chief State School Officers (CCSSO) and The Learning Accelerator (TLA), is helping to seed the development of multiple full-course, high-quality open curricula.

LearnZillion, where I am a co-founder, is one of the finalists for this initiative. We are developing a full, K-8 math curriculum by breaking the barrier between publishers and teachers. Our authors are a “Dream Team” of 140 math teachers from 38 states. Each of the teachers was selected for his/her content expertise, classroom experience, and teamwork skills. Nearly 4,000 teachers applied to the Dream Team, making it more competitive than getting into any college or university.

Once selected, each teacher is placed on a five-person team led by a math content expert. The team is responsible for building a set of unit plans that fit, like Lego pieces, into a larger curriculum framework.

The user experience of open curriculum will get much better

As the number of options expand, so too will the quality of the experience. One of the big limitations of open resources has been the user experience. Until now, open curriculum hasn’t been able to take advantage of the web’s power to make difficult, time-consuming things (paying bills, sending holiday cards, buying gifts) happen at the click of a button. Even the EngageNY curriculum is paper-based. Teachers must download large PDFs and read them like old-fashioned instructional manuals.

I keep remembering a line from Peg Tyre’s piece “iPads < Teachers,” in which a teacher talked about the clunky education technology around her:

“It’s like the printing press has been invented,” said one teacher in New Orleans wistfully. “But the great books have not yet been written.”

In contrast, a cloud-based, digital open curriculum will be digitally “native.” The curriculum we are creating at LearnZillion, for example, is responsive to any screen, uses videos to introduce lessons and summarize the core concepts, allows teachers to assign any part of a lesson to students online, and automatically shows teachers how much their students have learned based on online practice and assessments.

Open curriculum is more teacher centered

One of the biggest benefits of open, digital curriculum is that it invites teachers to make changes to the lessons. We saw teachers doing this right away when we launched LearnZillion in 2011. Teachers downloaded the PowerPoint slides and made edits to customize the content. One teacher in Washington, DC created a parent connection document that could be sent home to help parents support their students.

Traditional curriculum makes these sorts of modifications and enhancements difficult. The approach has been, “Here’s the plan; follow it.” It is like a coach telling her players, “This is your playbook. Stick to it no matter what happens out on the field.”

Not only does the closed approach prevent teachers from better meeting their students’ needs, it blocks innovations. LearnZillion lessons now incorporate the parent connection that the teacher in Washington, DC developed. In fact, most of the improvements to our content have come directly from teacher insights born from experience.

The line between user and publisher is disappearing, which ensures that the curriculum becomes more and more useful to teachers.

Being teacher-centered also matters when it comes to curriculum adoption. Teachers are not the ultimate decision makers, but their voice in the decision-making process is growing stronger. District leaders don’t want to adopt products that nobody uses.

Curriculum is in the midst of a sea change. The days of expensive, closed curriculum are numbered. What is emerging will not only save districts money; it will tap into the collective expertise of teachers across the country. In five years we will say, “Remember when we used to buy expensive textbooks that didn’t let you adjust to your students’ needs?” It will be like saying, “Remember when you had to put film into your camera?”