Believe me or not but for a 101 bioinformatics course I taught this year, I picked up jslinux to teach grep, pipe and other shell scripting basics.
This was just the simplest option to get a linux prompt on every machine of the computer lab - and studenta who had brought their own laptops could work on the very same examples as the rest of the class, in an identical environment.
Busybox grep is good enough for teaching the basics to students, and they can access the very same setup from home if they want to rehearse or try to solve the problems in a different way. .
What is truly missing is not persistent storage but basic network support, to be able to wget example files. Not anyone can cook an initrd (loop mounted ext2 filesystem)