The materiality of the misrepresentation is a question too, since in rescinding a contract, an element is a misrepresentation of the level of materiality such that the other party would not have entered into the contract had the "misrepresentation" been known.
The big picture still eludes you. The contract theory you cite is less appropriate here than are the genral rules of evidence. There exists a strong presumption on the part of the applicant that the non-disclosed issues ARE material, otherwise they would have been disclosed. That presumption is created by the applicant when he lies or fails to disclose information on the application. Hence, the failure to disclose creates a rebuttable presumption that the school would not have otherwise admitted the applicant, because the applicant is, himself, assumed to believe so.
Besides, one could argue under the well-established contract law doctrines that an applicant who secures admission under false pretenses has committed fraudulent inducement
, particularly where he accepts and receives scholarship money that might have otherwise been given to another student. Secondly, you must understand that "relevance" and "materiality" are determined by their "probative value", i.e. their ability to make the truth of a matter more or less likely. The principle "matter" of C & F on a law school application is the trustworthiness (or lack thereof) of the applicant, as determined by his/her responses to the question(s).
By lying when queried about even the most trivial offense, one indicates a greater likelihood that he will mislead or outright lie when a more serious matter is at hand. One indicates that he is more likely to cheat on an exam, steal study materials or property belonging to another student, plagarize another's work, or falsely accuse or blame another for his own transgression. One indicates a greater likelihood that he will not disclose evidence that disfavors his case if he is a prosecutor, fail to disclose settlement/plea offers that only he deems inadequate, or misappropriate the funds of a client or the state.