Is there any negative effect from sending MIT a letter of continued interest?
I don't see why this can hurt your chances. Just make sure that you add something new to your application, and use this opportunity to make your application more personal (have in mind that RD students don't get to send this letter)
Best of luck!
I am not specifically certain about MIT, but if you send a letter of continued interest for any school I would just make sure it is not super basic and provides examples of maybe things they have have not already seen on your application (ex a new class you heard about, talking to an admissions counselor, etc.) just so it is not repetitive and they really see you are interested and have done work looking into MIT specifically, show you are really passionate! I hope this helps :)
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