You worked too hard to get into college to mess with it now. Seniors should bear in mind that their remaining high school grades can affect their new relationship with the college they plan to attend next fall. Colleges certainly do not like to renege on admission decisions, but will do so on occasion. This most typically happens when a student’s grades drop SIGNIFICANTLY. In other words, if an A student suffers a bout of senioritis and one or two grades drop to a B, it’s not a deal breaker. But if grades plummet to Cs and Ds, it can be. Historically, about one-fourth of colleges revoke at least one offer of admission each cycle, and the major reason cited is plummeting grades.
If there are extenuating circumstances behind a downward trend in grades (e.g., an illness or family crisis), these should be explained to the college in writing by the student and supported in writing by the school counselor. The college will probably be sympathetic and stand by their original acceptance. I have heard of a few cases when a college put a student on academic probation at the start of the freshman year.
Colleges may also revoke acceptances if the student is suspended from school or arrested outside of school. Again, because the college does not want to do this, the case will be carefully evaluated and the outcome will most likely depend on the nature of the infraction and the circumstances surrounding it.
Finally, if a college should discover that an applicant was dishonest on his or her application, they may well rescind the offer of admission.
Best wishes for the New Year and may all your admission news be good news!