I'm hoping to apply to some very selective engineering colleges, including MIT and Caltech. I'm a little worried about my ACT scores because I only got a 27 on the Reading section. This is six points below any of my other section scores. Will it hurt me in the admissions process?
A 27 on Reading is not likely to damage your admissions chances by itself, but a 33 composite score is slightly below average for MIT (34 is the average score). While your scores still give you a good chance of admission, I would recommend retaking the ACT if you have the time and resources.
MIT does superscore the ACT, so you can focus your studying on the Reading section exclusively. Even if your score drops by a point on one or two of the other sections, you'll be able to keep the original (higher) scores as a part of your official composite.
If you increase your Reading score by two points to a 29 instead of a 27, you can bring your composite score up to a 34 (assuming your other three scores don't go up by a point - they must be hovering around 35 right now). If you really knock it out of the park and get a 33 on reading, your composite score will go up to a 35. This is the ideal situation because a 35 is above average for MIT, so it will potentially give you a leg up in the admissions process.
If taking the test again isn't an option, think about how you can stand out as an excellent math and science student on the rest of your application. Heavily emphasize any achievements connected to these subjects. For more information on how to improve your chances at a top school like MIT, check out this article (advice applies to extremely selective schools outside of the Ivy League as well).