I took a one semester economics elective in high school where we made a pretend stock portfolio and tracked it's progress, learned about different economic theories, etc. The last day of class the teacher handed us a print out that showed compound interest - how much more you would have in 20 years if you started now, versus how much you would have if you invested double but didn't start until 10 years from now (or something like that). He said he didn't care if we remembered a single other thing from the class, but that when we started getting jobs we should always remember to save. I remember him yelling it out the door at us after the bell, as we leaving. It stuck with me.