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Senior grades play no part in the admissions process.</p>
<p>After acceptances/rejections are handed out, students send in transcripts only to the UC that they are going to attend. The transcript does nothing but confirm the courses and grades that you listed in the application. However, your acceptance can be rescinded by failing courses during your senior year.
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<p>As a California resident (very well acquainted with UC admissions), I can tell you this isn't quite true.</p>
<p>For most, midyear reports aren't needed. For some, the UCs may request a midyear report (augmented review, along with a questionnaire and even other additional information). However, at the end of your senior year, you must send in a final transcript. This serves two purposes: 1) they check the grades against what you reported on the application, and 2) they look at your senior grades. If your grades don't match up, your admission is rescinded. If your senior grades aren't up to par (at least a 3.0), your admission is rescinded. There have been cases in which Berkeley (perhaps UCLA too, though I've only Berkeley do this so far) rescind admission even though they met the "3.0 requirement" (and there were no discrepancies otherwise). There are also cases in which the student barely meets the requirement and they're put on "probation" (whatever that might entail). Remember: the offer from the UCs is what they call "provisional," not "official," pending your official grades. Not to mention scholarships to UCs often have a higher standard than the "3.0 minimum."</p>
<p>In addition, even if you meet the requirement, if you get below a C in an a-g course, you can become ineligible for UC after being accepted (provisionally). So you can get a D (not failing) and as a result be ineligible for UC.</p>
<p>In any case, this only happens at the UC you choose to attend. The others won't get your final transcript, so they won't be able to rescind admission, etc.</p>
<p>Regardless, senior year grades are still important. It wouldn't make sense otherwise -- UCs consider grades/GPA to be the most important, so they aren't going to just "ignore" your senior year, which is the closest to the terms you'll spend at the university.</p>