Mine was a page, 12 font single spaced. I took a college writing class in high school and this is what my english teacher told me that most colleges want/look for and like. It also ensures that a page doesn't get lost leaving admissions wondering what your conclusion is going to say.
A few other tips she gave me...don't write about anything sad/depressing. Tons of kids right about these kind of things and it is refreshing to read something other than what a death in the family taught me. If you do decide to write about something like this don't look for sympathy, keep it to the point.