For what it's worth and I don't recommend this solution to a lot of people...I can point out a way we're thinking of doing our 1 to 1.
Very controversial method but I'm in a K-12 school district and am seriously considering this barring any urgent warnings not to for our deployment. It involves using Casper to push apps out over the air.
https://jamfnation.jamfsoftware.com/discussion.html?id=7446
Students don't need Casper Focus installed. Student iPads just need to be enrolled in the JSS. The teacher is the one who needs Casper Focus installed.
My only caution would be that pushing apps out OTA through the 'in-house app' work-around is likely to cause problems in the future... As it is not a supported avenue from JAMF or Apple, I personally would say that the odds of it breaking at some point through any update or change is quite high. For me personally, rolling my own solution on iOS is too high of a risk as Apple has already demonstrated that they will break these sorts of things while the platform matures. That's just my take on it.
To the original questions intent though, Nick has that covered... You only need Focus on the teacher iPad.
Do Teacher Devices with Casper Focus have to be supervised? We've already supervised the student devices, but the teachers are unsupervised.
No, teacher devices do not need to be supervised. Unless you are planning on Focusing/locking teacher devices to an app.