WANT TO BE A DOCTOR? A SCIENTIST? AN ENGINEER? AN AFFIRMATIVE ACTION LEG UP MAY HURT YOUR CHANCES: A few days ago I overheard a couple of teachers (at least I think they were teachers) talking about how to encourage more minority students to pursue science careers. I almost broke in and told them. Instead, I am telling you: Nowhere is the evidence of the “mismatch effect” clearer than in the area of STEM. Whether it’s an affirmative action preference or a legacy preference, don’t take it if you want to major in STEM. Go to a school where your entering academic credentials put you at least in the middle of the class.