And don't be shy with it...at any age, they love the race. I have middle-schoolers...and some ultra too-cool ones at that...and they look forward to SuperSpeed 1000 big time.
Avoid the pitfalls I have made:
-- be sure you fully understand the 'rules' and methods of moving ahead before you explain it to your students
-- model, model, model the process of how to move ahead in the game so you're not running around explaining it to each team each time
-- USE TEACH-OKAY when explaining the rules and methods of the game so that students hear you say, and hear each other say that you START AT THE SAME PLACE ON BOTH TRIALS. It took my students quite a few mistakes before they really understood that, because they weren't completely listening (what? middle-schoolers??)
--don't 'fight with' the ones that refuse to really 'get into it'...just walk by, prompt or praise, and keep going. Don't stress...they'll come around.
Enjoy!