In our opening junior course we freuently used primes on variables to distinguish between two different variables. It wasn't until after we taught the course that we captured a student discussion where students expressed great frustration with this, because the only previous time they had seen primes was with derivatives. Thus students didn't realize that were simply looking at two different “r's” (for example). Instead students were often looking at equations and trying to figure out what a derivative was doing in a formula where it didn't belong. The students suggested using subscripts instead.

We have just become aware of the problem and have not attempted nor decided upon any specific ways to address it.

Video - 080220Ph424Main (not yet available to the public)