you could have them experiment with dektol, which is often used as a film developer.
it gives a different look than d76 .. they say 1:7 7mins as a starting point.
mad scientist thing with coffee ( caffenol C ) might be fun too easy to mix with teaspoons and no scales ( or exact measures! ) needed
it can give a look anywhere from just like d76 to grainy and foggy any pyroesque without the worry of chemistry used.
you can also add 1oz/32 of print developer into the caffenol .. it takes the edge off. i use ansco130 ...
good luck !
I haven't used anything but D-76... But john, you should make a stronger statement for caffenol. Especially since you have the examples to show what it can do.
This would be valuable as an eye-opener. See how little it takes to make a developer, this will open the student's minds.