Microsoft announced today that it has acquired Flipgrid, an education start-up that it had previously partnered with.

“Today, I’m incredibly excited to welcome Flipgrid to Microsoft,” CEO Satya Nadella says in a video announcement. “Together we have a shared mission to empower educators and students. Flipgrid is the place where students go to share ideas and learn together. And where educators go to engage them.”

Flipgrid is a sort of YouTube for education, where students can discuss topics using videos created at home or in the classroom and then respond to others’ videos with video replies. It’s in use by “millions” of students, educators, and families in over 180 countries, the company says.

Microsoft first partnered with Flipgrid about a year and a half ago, but the results of the acquisition will have an immediate impact on any schools that are using the technology: Microsoft will make it available for free to all schools. And any educational institutions that were paying for the service already will receive a prorated refund.

That’s pretty amazing: Previously, Flipgrid charged about $65 per year for each educator and $1000 per year for each school that used the service. Microsoft also makes Office 365 Education freely available to schools. That level of service costs enterprises about $150 per year per user.

One potential rub is that Flipgrid works well with the Chromebooks and Google services that currently dominate the education market in the U.S. and elsewhere. But Microsoft says it is committed to ensuring that Flipgrid always works well with the Google ecosystem too. The goal is “to benefit students and teachers everywhere,” it says.

Microsoft also notes that it will announce new Flipgrid services in early August, so there will be more news on this front soon.

Tagged with Flipgrid, Microsoft Education