Don't know what the OP was doing, but schools operate with different rules for licensing. Some scenarios that aren't possible for individuals or enterprise are possible for schools, depending on the agreements in place.

Mostly Windows 10 - supports even 32-bit CoreDuo, all edu software works, staff knows it. In EU you can buy second-hand software licenses legally. Some schools participate in volume licensing schemes with MS too.

But I also install Ubuntu on some specialized "workstations", e.g. pendrive/Internet terminal laptop connected to beefy old laser copier/printer where CUPS PCL works with zero drivers. Other use case: jukebox laptop for music classes :)

Mostly likely Windows because most education software is written for it and most education places get it basically for free.