A free way to shoot Aliens: http://sbtf.nornware.com/
Unlimited ammo plus motion sensors against aliens = You're going to die. :)
(Found via http://www.rockpapershotgun.com/2015/01/14/roguelike-aliens-fps-space-beast-terror-fight/ )
You're going to sneak this into your curriculum, aren't you? ;)
Wow, that looks like it could be a lot of fun! O0
I'm sold by the words "procedurally generated space beast terror fight".
I'd be tempted to sneak it in :) but it seems to require an internet connection so it can update itself or something (and for the initial download).
Galaxy Monster Horror Brawl
Interplanetary Creature Scare Altercation
^-^