Do you mean other than just using the variables available? For instance, I display the Full Name, Email, and device Serial Number on the lockscreen of each our iPads using these variables. Documented here:
Which is also available as a blue link you can click on when you're configuring the Wallpaper settings in a config profile in Jamf School.
Maybe I'm misunderstanding what you're asking for?
I start off by going to https://www.apple.com/ipad/compare/ to grab the dimensions for the iPad screen I need to create a wallpaper for, then reflect those dimensions in Keynote or Pages. While there are more sophisticated programs available, these will do the job (for free). Figure out all of the variables you are going to display on the iPad with a few tests, and design your "variable box" size from there. I know this can be a bit tricky if you pull in FirstName, LastName, Email, etc, since it will be different for each teacher and student.
If you'd like to get a bit more generic and web-based, you could check out sites like canva.com. I'm not sure about their pricing or licensing overall, but it's another great, easy tool for making wallpaper!