Cull information from your past four years in school. You will want to have all of the info handy before you write, so you don't leave anything out. Write an outline, starting with your freshman year through your current grade. If nothing life-changing happened, move on to things that stick out in your memory -- your first A+ in German or your first F in algebra. Anything that affected you is fair game.
Begin your essay as you would an obituary. "Jane Smith's high school life died 7 p.m. Thursday of natural causes. Born in the fall 2006, Smith's education blossomed early, with classes such as AP English and history, as well as advanced math and French."
Expand on your classwork. Depending on what your scholarship essay is intended for, you should focus on the most pertinent subjects. If you are applying for a scholarship from a veterans committee, make sure you focus on your interest and successes in your history and sociology classes. If your essay is meant to get a scholarship for biology, tell how your first experience dissecting a frog went.
Include important extracurricular activities. If you are involved in band or choir, include this to prove you know how to work as part of a group. The same goes for scholastic bowl or football. Also include any volunteer work you've done. Make sure to tie this in as part of your obituary -- saying that with your high school life's death, the death of these activities has come as well; however, the lessons you've learned through the activities will live on in the new part of your life.