For months, Stanton Elementary School teachers and administrators searched books, webinars, conferences, news articles and anything else they could get find for ideas about how to get students more engaged in the classroom.

They kept running across the same mysterious two words: blended learning.

“We didn’t really know what it was,” says Principal Caroline John, “besides computers.”

Fast forward a year, and the same 400-student public school here in Southeast Washington, D.C., with its green-tiled halls and pastel stucco classrooms, is defining the phrase on its own terms. And at least in this case, it's not that complicated.

At Stanton, students in grades 3-5 spend 45 minutes a day on an iPad or a Dell laptop working on ST Math, an online math program that challenges each student based on his or her skill level. For example, one student could tackle multiplication tables, while someone in the next row completes double-digit addition problems. Some do all their work by typing and touch-screening their way through problems and solutions, while others swivel between scouring the screen and scribbling on scrap paper. Teachers rotate through the room, helping students when they stumble on a given problem.

Time runs out, the devices are packed and pushed to another classroom, and the rest of the day proceeds with nary a computer in sight. But the straightforward structure of Stanton's blended learning program is just one example of blended learning’s loosely organized front that, despite wide variations in individual practice, appears to be quite powerful.

“Just in the last few years there's been tremendous interest by school district leaders who know they can't keep doing the same thing and expect different results,” says Susan Patrick, the president of the International Association for K-12 Online Learning, or iNACOL. “We're absolutely seeing a trend toward blended learning.

Because there's no firm dividing line on where exactly blended learning starts and stops, it's hard to identify just how many schools nationwide are practicing it. “Keeping Pace,” an annual report that examines online and blended learning, estimated that two-thirds of the nation’s nearly 14,000 school districts offered some sort of blended learning option in 2012, though it adds there is still plenty of room to grow in terms of how many schools or students utilize those programs.

A big reason for its growing popularity, Patrick says, is that, despite the increasing capabilities of educational technology, most students and teachers still prefer real, live interaction over completely online learning.

Further, to understand blended learning, it's crucial to understand what it's not: doing online worksheets, reading digital prompts or any other technology-related activity aren't examples of blended learning unless they allow a student some control over the pace and content of the instruction.

“What I want [people] to think of is students having online learning for part of their day and brick-and-mortar school for part of their day, where the student has some personalization,” says Michael Horn, a blended learning expert with the Clayton Christensen Institute.

At the Christensen Institute, formerly the Innosight Institute, Horn and his team have evolved from mere advocates for blended learning to catalogers of its trends and commonalities. In May 2012, the organization released a white paper that broke blended learning into four categories: rotational, flex, self-blend and enriched virtual.

Stanton and many other elementary schools fall into the rotational category, where students alternate between working online and working in a traditional classroom during the same course of study, usually math or English/language arts. High schools are perhaps the most likely to operate a self-blend model, where a student takes one or two online courses—often Advanced Placement or credit recovery courses—to supplement their in-class education.

The other two categories are a bit more specialized. The School of One math program in New York—which gives each student a uniquely tailored schedule of online lessons, group work and traditional classroom lectures—was an early example of a flex model. Enriched virtual models include any school where students get most of their instruction online, but periodically meet with a teacher or teacher aide.

While there are subsets within those four variations, Horn believes that as blended learning continues to popularize, educators will gravitate toward one or two most-familiar models, likely rotational and self-blend.

Already, there are some titans in the field, like Rocketship Education. The nonprofit educational management organization currently operates seven rotation model charter elementary schools in Silicon Valley, and is also set to expand to Milwaukee and other cities across the country. Big-name philanthropies have also taken an interest. The Bill & Melinda Gates Foundation, for example, has devoted millions of dollars toward promising secondary education blended learning models via portions of its Next Generation Learning Challenges grant competition.

Supporters also note that that a blended learning model might be of great benefit in a school where layoffs have boosted class sizes, or where demographics lead to wide disparities in student abilities in each class.

“To be able to help a teacher serve a student at a first-grade level and a student at a fourth-grade level at the same time, that's what we're excited about,” says Mieka Wick, the executive director of the CityBridge Foundation, which helped to bankroll technology purchases related to Stanton Elementary's blended program, in addition to several other uniquely structured blended learning efforts in D.C.

That said, even blended learning's most ardent proponents warn that the field is too new to know everything that works and everything that doesn't. That need to gather more information is one reason CityBridge is supporting a range blended efforts in D.C., including an algorithm-driven program called Teach to One at Hart Middle School, created by School of One founders Joel Rose and Christopher Rush, and a blended learning fellowship that is giving 12 teachers training to launch blended pilot programs at their respective schools.

One approach most agree is bound to fail, however: focusing on the hardware or software.

“We don't talk about products at all during our process, we talk about what we're trying to achieve,” says Anthony Kim, the founder of Education Elements, a consulting firm that helps schools, districts and school networks create blended learning programs.

“It gets very confusing for these folks,” Kim added. “I think people come in with a diagnosis of what they want—‘I need an iPad’—but they're not talking about what kind of function they are trying to solve for. It's like a patient coming in asking for drugs without being aware of the side effects.”

It will be months, or even years, before the staff at Stanton can identify whether their program is having long-lasting effects. But the school, once on the brink of shutdown in 2010 for poor performance, again has the trust of its students and parents after doubling its percentage of students proficient in reading and tripling its percentage of students proficient in math over the past three years.

Principal Caroline John says any additions next year to the blended program will be small ones, like the possible opening of the school's first computer lab, or the inclusion of some reading-related software. And she says educators who want to go blended gradually should be unafraid of falling short of the big shiny programs like Rocketship.

“That can feel really overwhelming and intimidating to even think about.” John said. “But one thing we've learned is that we can, step by step, add pieces of blended learning.”