I teach Computer Science at the High School level (as a second career).  We use PICO's with a Display Pack connected (see my case: 

https://www.printables.com/model/745130-pimoroni-display-pack-case-with-cutouts-for-picow

I needed a way to organize them so the cables didn't get to tangled, and I could tell if all of them were turned in.   There are 4 files, a single standalone (stores 5).  Then we have the left, right and center versions.  Each handles 5 units.  Put a left and right together for 10, or add center for 15, or more.  The left right an center have dovetails to hold them together.  There are also screw holes to help mount.  I'm using some foam tape due to the concrete wall.

NOTE:  This was designed to fit PICO's with the Display Pack and the above listed case.