Colleges will probably NOT contact your high school for grades in mid-March unless you are a borderline applicant. If you are, admission folks will want to see if your senior grades are as strong as—or stronger than–your past ones. Likewise, they may ask for grades if there’s some specific concern that the March grades might resolve. For instance, if you had a light junior course load and are taking more rigorous classes in grade 12, the admission committee may want to find out how you’re handling the challenge.
If this question you’ve sent to “The Dean” is code for, “I had a good first trimester but already I’m starting to slack off, and I worry that my second trimester grades may screw me,” rest assured that you could get lucky and your admissions verdict might be issued without the March report card … or you may get unlucky and the downturn could hurt you. Keep in mind, too, that colleges will rescind acceptances if final grades aren’t up to snuff, but they usually give students some wiggle room to falter in the spring, as long as it’s a small slip and not a crash-and-burn!