What to do with helplessness?

This week I became frustrated with my Geometry students who don't know how to take a cube root on their calculator. We have already done this when we did similarity and looked at area and volume of similar figures and now we are doing some more complicated volume problems. Why can't they do this? One reason (I think) is that they really don't have a calculator of their own. There is no reason they can't own one, I teach at a private school and most of them have Smartphones, IPods, IPads, etc. I stopped providing calculators (because they disappear and I find them hard to keep track of..... Hmmm. I show it to them two ways using the cube root function and raising it to t he 1/3 power (reminding them to use parentheses).