Advice for a high school student
paulgraham.com
paulgraham.com
About realizing the need to get things done, there's a window that a lot of people don't notice. It opens with said realization and closes when it's too late to act on it (you could say it never closes, but having kids certainly makes things harder). So a lot of people spend much of their 20s and early 30s lamenting their wasted youth without realizing that they've still got time to fix it.
While this knowledge would be extremely beneficial for any student of any age, I think the primary difficulty would be in actually feeling the message, as opposed to understanding it. Everybody knows "practice makes ___," but few people act it. The ultimate challenge would be to convey that feeling. Something I'm very interested in :)