Classrooms often use interactive whiteboards driven by PCs that can be quite slow to log in to the teacher's active directory profile as this involves pulling data over a network of variable speed. There can also be issues with software upgrades deciding to start at random times. The PC will need to be logged off and logged on 8 times a day...

Teachers don't talk to themselves in classrooms so time loss can affect a small percentage of up to 180 student-hours per day or 900 student-hours per teaching week per teacher. A typical '8 form entry' secondary school in UK will have around 100 teachers plus admin / head of subject / 'leadership'. School year is around 38 weeks.

I sometimes think something like ChromeOS but that can run IW software and just stay booted would be better. An appliance.