A deferral means the Admissions Board has initially reviewed your package but needs additional information before making a final decision. That info could include first semester grades, new ACT/SAT scores, etc.
Clearly, your next set of grades will be important. In particular, they may be looking for a grade in calc, chem or physics, especially if it's at an AP level. An "A" will obviously be great. A "C" will hurt.
Has anyone received an appointment after being deferred? I've been searching past posts but can't find anything on the topic updating deferred status.