<p>While the OP asked about the SSAT or the ESSAY, the truly most important determinant is GRADES/TRANSCRIPT and RECS. The grades tell a school about your past performance which is the best predictor of how well you will do in the future. The recs tell about you as a person, student, and member of your school community. So do your best on the SSAT and the essay, but spend the most time on your school work!</p>