The goal of school education in computers is not to prepare pupils to use commercial software and become better consumerists. They already know how to use commercial software anyway, most of them even better than their teachers. What they lack and need to learn is the fundamentals of how computers work, how operating systems work, what safety and security means (especially online), and the basics of programming. In a nutshell: No, Windows is definitely not needed or desirable in schools. To be fair, iPads and Android tablets are even less useful, because it is almost impossible to teach programming on them in a fruitful way.
I'd even go farther and state the obvious that commercial software packages should be banned in public institutions entirely when there is an acceptable free substitute for them.
To give a typical example of how Windows computers are used in such environments, our institute at a public university in Europe has dozens of +5 years old PCs that are overloaded with tons of viruses and trojans and the crappy paid anti-virus we're using fails to detect them. The machines have become even slower after they had to be upgraded from XP to Windows 7 recently. I've test run Ubuntu on one of them for years and it worked better and faster in each and every respect except compatibility of LibreOffice with Word (which is broken intentionally by Microsoft, but strange enough it also breaks routinely between versions of their own software). The tax payer is paying huge fees to Microsoft with no benefits at all - and you have to check your USB stick for viruses each time you've used one of those machines.