I am attaching a breadboard picture and a crude schematic, which has the motor connected to 3.3V as I believe you are using a 3V pager motor, yes?
You can have the students breadboard the project without the Hall Effect sensor like this:
*Run the wire from D12 to +5V to simulate the wheel being out of alignment.
*Download and run the code. The D13 (READY) should be OFF, indicating that you aren't ready to start.
*Move the D12 wire from +5V to GND, which simulates the magnet aligning. The D13 (READY) LED should come ON to indicate that the wheel is now aligned and we're ready to go.
*Press the GO button. The motor should start running.
*Now move the D12 wire between between GND and +5V ten times.
*After the tenth transition from HIGH to LOW (this number is a constant in the code), the motor should turn OFF.
You can test the setup and get everything working so that, when the Hall Effect comes in, you are already 90% done. Be mindful of the heat of the motor. It might
not like running for more than 30 seconds or so.
The breadboard pic is generated by Fritzing here: http://fritzing.org/