My $0.02... think of some event in the past that really caused you to question or contemplate life and then write about the emotions you felt during that process, how you dealt with them and the actions you took to overcome such event, and whether or not you think you handled it correctly. But ultimately how it motivated you to be a mature adult that can handle future hardships while accepting responsibility and the ability to learn from those hardships to become a better person. If all you have is moving away to boarding school then so be it, but there's most likely something you're not thinking of, as I've yet to meet anyone from Pleasantville or the Brady family.
IMHO I think adjusting to a new school environment (especially one that is served up on a silver platter) is less of a challenge and more just being forced out of your comfort zone, which is just the natural process of childhood development whether privileged or poor.