Like everyone else, I've tried various ways to dispel this rumor: we've drawn models, we've used models, we've discussed. Seemingly to no avail. This year, I tried yet again with a different tactic.
We started out with a rectangular prism 3' x 2' x 4'. They found the volume in feet cubed. Then I asked them to find the volume in inches cubed, and to a person, they all wrote the wrong answer (24 x 12 = 288). Then without saying they were wrong I had them go back and redraw the prism into the inches equivalent and recalculate the volume, and OH NO, they were wrong with their first "288". Hmmmmm. So, this is stuff I've tried before. Now for the "new" attempt that MAYBE will work.
I had them write: 5 ft^3
Then change to: 5 * ft * ft * ft
Then EACH foot had to be converted to inches, so
= 5 *
= 5 * 12in * 12in * 12in
= 8640 in*in*in
= 8640 in^3
Let's see if this one sticks.