Not easily. In my opinion, you're unlikely to be able to get the cost/performance/multiseatedness that you want. In short, there's no way to do this.
There's a few elements here - 'Desktop' windows only lets you run a single user at a time (windows server will let you run more sessions at significantly greater cost), windows dosen't work multiheader (and the NUC dosen't really have enough ports), and well, most of the options I can think of probably suck, or are more expensive.
If you arn't tied into windows, you could probably use something like a raspberry pi or other low cost, small form factor single board computer- either as a standalone system (Raspberry Pis seem perfect, other than the lack of VGA ports - you need a HDMI or composite capable display or a converter. Even then, you can get 4-5 pis for the price of a low end nuc). There's also multiseat linux setups, but between needing multiple video outputs, and so on, not worth the effort. Get cheap, get lots, and get going.
The fundamentals of learning to use a computer carry forward completely well between OSes, get them started on linux, then if needed, they can probably pick up windows fairly easily (I went the other way myself).