I learned computer science for four years in high school. One of the teachers didn’t know what arrays were for at one point, but if we had had somebody who was any good at programming, or teaching, or preferably both, I really wish they’d shown us this: Sorting algorithms. All sorts of sorting algorithms. Done visually! With added sound! I have never felt more tempted to run off and learn how they’re done and how quick each of them is in my life.