Protecting Arduinos from Students

So, I teach middle schoolers (7th and 8th grade, 12-14 year olds). I am doing a unit using the SparkFun Inventor's Kits, which use the SparkFun RedBoard as their Arduino. Link to the RedBoard here.
The point is that I obviously don't want my boards destroyed by the students. As far as I can tell, with my basic electrical knowledge, there are only two ways my students could destroy the boards, given what we are doing with them. As background, we are only powering them by USB, never an external power source.

Situation #1:
The student is trying to turn on an LED. They accidentally connect both wires to the same terminal strip so when the LED is turned HIGH, the electricity goes straight to ground.

Situation #2:
The student is trying to alternate turning on two LEDs. The student connects them in series and then connects one end of the series circuit to pin 13 and the other end of the series circuit to pin 10 and then tries to alternate turning them on and off. This causes the electricity to flow out the HIGH pin and into the LOW pin (this seems like a pretty unlikely scenario, but I learned long ago to not be surprised by the variety of things my students could get up to.)

Anyway, my questions are:

1. Is there any way to prevent these situations short of telling the students "Don't do that!"?

2. Does the fact that they are getting power via USB change anything?

All outputs should have a R in series to limit the current. For a LED it should be about 220 Ohm's.
Never have LED directly from output to Gnd or 5v.

To alternate LEDs, use two outputs (one for each LED) and drive LEDs to Gnd via a R.

Weedpharma

There's some info on the various ways to harm an Arduino and methods of preventing it here: 10 Ways to Destroy an Arduino — Rugged CircuitsRugged Industrial Arduino Microcontrollers. Your scenarios are the top two. Their solution is a PTC, which also provides the resistance. I suppose you could make a shield for your boards that adds some protective components.

dgebhart:
2) Does the fact that they are getting power via USB change anything?

It means there will be no voltage over 5V available, eliminating one possibility for damage.

Situation #2 will not pose an issue (assuming there is the above mentioned resistor). Shorting an output (situation #1) does pose an issue.

If I was the teacher, I would check the circuits before the students are allowed to power the board; doable for a small group, problematic for a big group.

The only way to protect the 328 micro is by adding current limiters in some way. The rugged arduino (no idea of the price) might have been a better choice if you're worried about students doing things wrong.

I have made wiring mistakes with the Sparkfun Inventors Kit and till now the RedBoard has survived; can't remember how potentially 'dangerous' the mistakes were. But if code did not work as expected, I immediately disconnected the board and checked the wiring again to make sure that it was not a wiring mistake.