How is it used in exams?
While this may be a tad short-sighted, it is a legitimate concern. Teachers simply don't have the resources to constantly be monitoring a class of students to be sure that they are not accessing the internet or communicating with each other (which is fairly easily fixed in settings).
The greatest part of iPad technology is the connectivity. They have the potential to facilitate inter-actions between students and their thoughts.
A friend of mine introduced me to the solution: Guided Access.
Guided access is a feature where the teacher can lock the iPad into a specific app. It requires a passcode to get out. It even has the ability to disable certain portions of the screen. (I'm not sure how this would come in handy for Desmos, but may work for other apps).
How to Enable Guided Access
Turn it "On".
Also, turn on "Accessibility Shortcut". This will enable you to triple click the home screen to change settings.
Close Settings and open up the app you want and triple click the home button.
The menu will appear, and click Start to lock the app.
If a student tries to leave the app, they will be prompted to enter the passcode. If they enter an incorrect one, it makes them wait 10 seconds to try again, then 60 seconds, etc.
On top of that, triple-clicking and the entering passcode allows you to draw on the screen where you would like it to be disabled. In the same screen, selecting Options allows you to disable touch and motion altogether if desired.
If you want to end Guided Access, simply click End.
This allows you to open Desmos, engage Guided Access, and (temporarily) limit the connectivity of the devices.
See this post for more details about Desmos and standardized test use.
This setting--also great for occupying young children--alleviates the worry of academic dishonesty and arms our students with powerful learning tools.