The robot my students are currently making is acting odd - as soon as you turn it on, it starts moving backwards by itself. However, the motors are attached to motor controllers, so this shouldn’t be happening. Here’s an explanation of how they wired it:
There are two motors to each side of the drive: they are first individually connected to a motor controller, and then a y-cable is used to wire them into the same port.
Could this be a problem with the motor controller? If the motor controller stops working (since I can’t determine how used they are or if they’re functioning) will the motors act as if there isn’t even one in the first place?
In my experience, broken motor controllers simply don’t send a PWM signal to the motor; the motors shouldn’t be moving at all. Your motors are probably moving backwards because of a program that was already loaded onto the cortex. I’m not completely sure about the default code, however, but if you want the motors to more forward you could plug the motors into the motor controllers backwards or just make a new program and download it onto the cortex.
Motors rotating continuously are one possible symptom of a 2-wire motor plugged directly into a 3-wire port. Make sure the y-cable is a 3-wire Y, and it is all really plugged in the way they told you it was. I’ve found that teen-age confidence levels are uncorrelated with the probability that things were done correctly. 
I need to stop looking at your posts from my office. I just laughed out loud…