The next big trend in education could be mixed-grade classrooms with personalized instruction — the modern-day one-room schoolhouse, essentially.

A traditional private school might sit on a sprawling, leafy campus with hundreds, if not thousands, of kids separated into grade levels. The "micro school" model turns this on its head, bringing students of all ages into the same classroom and using technology to cater the curriculum to each child's needs. Teachers serve as facilitators, rather than lecturers, and kids learn through projects, not memorization.

There are usually no more than 150 students enrolled in a micro school, with fewer than 15 kids in a class. And when a class grows too biges, the administration will often expand its network with more tiny schools, instead of raising the cap on class size.

Education Week's Arianna Prothero recently published a thoughtful explanation on why micro schools could create serious competition in the private school world. It boils down to two key factors: personalization and cost.

An AltSchool student writes an entry in his blog. Melia Robinson/Tech Insider

Many micro school evangelists believe the small class size empowers teachers to customize lesson plans for kids.

One such advocate, Max Ventilla, left Google as head of personalization in 2013 to found AltSchool. The San Francisco Bay Area-based network of micro schools enrolls between 80 and 150 students at each of its locations, and uses technology to tailor its instruction.

Teachers share lesson plans across the school's online network, and students complete tasks that are cherry-picked from this pool based on the learning strategies that work best for them. A digital "personalized learning plan," or a set of goals for each child, allows them move at their own pace.

AltSchool opened first outpost opened in Manhattan last fall, bringing the total number of schools to six.

Classrooms at AltSchool are treated like stations, rather than designated areas for particular grade levels. Students move from room to room throughout the day. Melia Robinson/Tech Insider

Part of micro schools' appeal is their cost.

"With small buildings, few faculty and staff members, and a curriculum built largely around free, online programs, micro schools strip education down to the bare essentials," Prothero says.

At Acton Academy, a Montessori-style micro school network launched out of Austin, Texas, tuition runs about $10,000 per year. That's on par with the national average cost of attending private school, which is $9,518, according to Private School Review.

Tuition at AltSchool soars to $25,000 on average, which Michael Horn, cofounder of the Clayton Christensen Intitute, tells Prothero is 10% to 15% cheaper than the average private school tuition in San Francisco.

It's unclear how many micro schools exist, Prothero notes, since the National Association of Independent Schools doesn't track them. At the very least, we know they've popped up in the San Francisco Bay Area; Austin, Texas; and New Orleans.

AltSchool students wait for their Uber cars to arrive and deliver them to a field trip. Melia Robinson/Tech Insider

Don't expect cost to be a micro school perk for long. As micro schools become more popular, elite micro schools will inevitably emerge and drive up the cost of an "affordable" private education.

Still, the ability to attend to students' needs marks an important shift away from a broken education system that forces teachers to teach "to the middle" or "to the test." Micro schools offer a promising solution — at least for those who can afford it.