http://www.inpharmix.com/jps/PID_Con...ms_Robots.html
Really good write up of PID used to Line Follow on a FLL NXT. I was able to use this guide, and get two 6th grade programmers to understand PID, and program one in NXT.
We also did this in Labview with the NXT toolkit 2 years ago when we made the step up to FRC, and needed to learn the basics of Labview.
Really helped when the autonomous our first year in FRC was line following for Logomotion.
Neither student has Calc yet, but both have a grasp on PID, and tuning K's.
[EDIT] {Remembered we really only programmed a PI for the line follow, it was very good, and we also learned to zero the I term when the error changed signs. }