Candidates should thoroughly explain their interest in a specific school by developing arguments that center on academic and environmental attributes (e.g., research institutes, professors, experiential learning opportunities, classes, pedagogies), but candidates should definitely not identify rankings as a reason for applying. Prospective students, administrations and alumni all pay tremendous attention to rankings, but in an application essay (and in interviews), the topic is entirely taboo.
Why? Rankings are a measure of a school's reputation and tend to fluctuate from year to year. By citing rankings, you are indicating that you could grow quite dissatisfied by a drop in prestige, as conveyed by such rakings, that is out of the school's control-a drop that, from the school's perspective, could put your relationship, as a future student and later as an alumnus/alumna, at risk. Further, schools want to be sure that you are attracted to their various academic offerings and that you have profound professional needs that they can satisfy. Rankings, however, are superficial, and referencing them in your application materials undermines the profundity of your research and motives.