Hi! (a little long - kind of got really passionate - but I'm just here to help)
Honestly, I truly believe that (especially during this COVID period, with they know have been hard for everyone) Harvard can be very forgiving in some cases when it comes to A's and a few B's. Remember, Harvard isn't looking for the "perfect" student: they're looking for a "well-rounded" student. Harvard is interested in someone with personality and interests, since it's all about breeding leaders and thinkers. You could be taking 20 AP classes and passing with flying colors, but if all you do is just study non-stop, what's stopping them from taking someone else who is taking 21 classes and might do volunteer work for the community? So, yes, I'm sure that a few B's wouldn't hurt your chances, you just have to make sure those few B's don't turn into multiple B's. Now in regards of bettering your chances into getting in Harvard, you're in 9th grade, so you're in a great position. You still have to the opportunity to go out and try for clubs and sports in later years, and you can start now working on your future Harvard essay. The Harvard essay is probably so important, because it shows them a little bit more of your personality aside from all the classes you take (the essay is so important, Harvard has literally published a book of the best essays they've ever gotten as examples). Also, pro tip: I know Harvard has you write "optional essays", but they're not really optional, so just do them. It shows your personality much more. Just remember to breathe, and remember that Harvard wants a "well-rounded" person, and those type of people might not get straight A's all the time. Harvard would be lucky to have you.
-Hope this helps!
Overall, since you are a freshman, I wouldn't be too worried, but if you continue to have B's throughout your four years I do think it would affect your chances. Even with your B's now, your gpa has lowered, so as long as it doesn't go much lower than it is already I think you should be fine (assuming you have only 1-4 B's right now). The average gpa for Harvard students is 3.9.
I will be a freshman next fall so don't take my answer too seriously. Colleges might not really care what grades you get in your freshman or sophomore years but the junior grades and senior grades will matter a lot. It's fine that you have B's now but in the future, you may have to get A's for Harvard to really think about accepting you.
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