Students report admission rescinded every year do to various reasons and it is a hard lesson that there are no ‘undo’ button in meeting requirements for college. Your minimizing the issue is not helpful and he in no way should reflect that dismissive attitude in his appeal. Not submitting transcript for every college borders on academic dishonesty. After all the college does not know what is on it, whether it has disciplinary actions on it, failed classes etc. Why he took it and what his own motivations were is completely immaterial–college classes are a permanent part of your record.
So first you say he didn’t send it, then you say he sent it only a week late. So I don’t know how to word an appeal, not knowing if they have the transcript or not. Just ask politely for reinstatement and express responsibility at not being timely in the initial submission of materials required for admission. Reaffirm interest in UCSC.
@EllenZL I can’t understand what your issue is. What it sounds like was that you didn’t report your grades correctly in the first place. Was it that you didn’t report the correct grades on the application as was shown on your transcript? What did you think you were going to do if you didn’t ‘let’ your school send your transcript? They still need your transcript no matter what.