Beginning in the 2008-09 academic year, there are two essays in the online graduate application.
The personal history, situated in the middle of the online application, provides an opportunity to discuss the cultural, economic, academic, and otherwise personal experiences and influences, including diversity issues, that would allow the University to discern aspects of diversity in the applicant pool. For MAT or teaching candidates, this is the place to talk about an inspirational teacher, a cultural influence, etc., especially if educational opportunities were scarce and challenges were overcome.
The statement of purpose is meant to generate a description of one’s academic or professional goals based on the fit between your intellectual interests and the intellectual work of the program and the professional goals you have as a teacher. Since it is not uncommon for one’s personal history to play a role in the formation of your sense of purpose, don’t be concerned if you repeat some things from the personal history section of your graduate application.