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.
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