One of these four numbers does not belong with the other three: 8, 27, 64, 100. Which one is it?

8 = $2\times 2\times 2,27=3\times 3\times 3$ and $64=4\times 4\times 4$, so three of them are perfect cubes. 100 is not a cube, so it is the odd one. Many students pick 64 instead because it is also a perfect square $(8\times 8)$ and so 'feels different' — but being a square as well does not stop it being a cube, and a square/non-square split would leave two numbers on each side rather than three and one.