Thank you for your encouragement. I have decided after reading a dozen pages from
http://robots.stanford.edu/papers/thrun.mapping-tr.pdf
that the system required to know the location and velocity of my Robocar at any given moment is beyond the capabilities of our 7-12th grade Public School STEM students.
As you can see in the video, above, my self guided Robocar goes pretty fast. The code is a state machine based on moment-by-moment readings on the forward pointing and right side pointing sonars. The kids can manipulate the five parameters in the C code that dictate at what distances and in which state the car should turn, brake, reverse, go fast.
Thanks again!
Ken