What’s happening is that the Windows USB boot image assumes that you will have a computer with an UEFI Bios. What we have with LC230 with Coreboot is they would call a “legacy BIOS”. That could be one reason why the USB does not boot up.
I think once the Windows installer is able to boot up, it would install just fine. The issue now is how to boot the installer without UEFI.
One quick thing you could try out is to boot the Windows installer using Ventoy.
Download Ventoy on your GNU/Linux installation. The Ventoy download page provides binary releases that you could just use. The same is available from their Github repository: Releases · ventoy/Ventoy · GitHub
Install Ventoy to an empty USB disk. Then just copy the Windows ISO image to the USB disk and boot the computer using USB disk. It should show you an option to boot the Windows ISO. I think the Windows ISO would boot fine that way.
Ventoy is essentially Grub2 with a set of scripts that search the USB for image files and present them in a boot menu for you to choose. The Mostly Harmless USB Disk is built using Ventoy. I could send you a unit and you use that too.
I have personally never tested this out but hopefully the Ventoy approach will work. Will look forward to your feedback.
Also check out this page: How to install Windows in Legacy mode - fit-PC wiki
Another option could be to give the computer to the school kids with GNU/Linux installed on it. If you just show them once, they might be able to learn how to do everything they need to do without Windows too. That might help them explore and learn a whole lot more.
If you need help with this aspect, I would be glad to pitch in whenever any help is needed to teach to something that is GNU/Linux related.