Can an American University take back their admission decision after?
Yes, your acceptance is conditional (look at the wording of your acceptance letter), meaning that if youre in high school, theyre accepting you provided that you continue to do well academically, pending receipt of your final official high school transcript. If you slack off and your grades drop, or you fail a class or two, they have reserved the right to revoke their offer of acceptance. Many do in cases where the seniors goofed off and didnt study. There are wait-listed students who did continue to do well, and who can take the seats of the slackers.