Hi, if you want to show your circuit prowess as well, and show that the real world sometimes needs buffering, you could use the Everyman's Chip: the 555.
This is billed as a Timer, and it is often used for that, but it has a nice 200ma output rating, driving both high and low. You can use 5V power (not the 12V on the diagram) and have a nice strong signal to send around the Lab, and protect your Arduino from short circuits etc. Just this simple:
BTW you can also use 12V or higher power and have your Arduino drive it, so it's also a Power Buffer. Sometimes it's used to drive high power FETs which switch 10's of amps.
Any electronics lab or guys you know should have a few 555s, even Radio Shack.
DISCLAIMER: Mentioning stuff from my own shop... which contains all the stuff I think is cool...
...Or you can buy 8 of them for $10 from me. Which sounds ridiculous
Except they are part of a big assortment for the 10 bucks, which includes 71 other popular chips.
I also make up kits for schools and Universities and Maker groups...
Hope your class has fun... The fact that you are considering error checking (Not taken seriously enough by most Arduino coders) is a good sign you're serious.