Question: My son is applying to some top colleges (MIT, Harvard, Princeton, etc.) with an intended major in engineering. He has two teachers in mind to write recommendations--one from an honors math class (he will take an AP class in senior year with the same teacher) and the other in AP chemistry, both 11th grade teachers. Is this advisable, or should he choose one teacher from a history, English, or language teacher?

Some colleges (e.g., MIT) require that applicants submit one recommendation from a math/science teacher and the other from a humanities teacher. I think that, in general, that's the wisest policy, even when it's not specified (unless the student feels that his humanities teachers are so heinous that he'd be shooting himself in the foot by asking them for endorsements). ;-)

In most cases, it's fine for a student to also send in one extra, unsolicited reference. However, ideally this should be from someone who has seen the applicant from a different perspective (employer, coach, community service adviser, etc.) and not just another teacher (who is likely to echo what the other two teachers already said) unless this teacher can also provide a new view (e.g., research mentor).

Your son should read all application instructions carefully to make sure that extra recs aren't discouraged and that he has adhered to specific requirements (e.g., engineering applicants to Columbia must include a reference from a math teacher). He might also want to present his selected teachers with a polite written request for the references that also includes a list of "highlights" of his time in their classes. Even though your son may remember forever that his European History teacher asked him to read excerpts from his term paper to the entire junior class, a busy teacher may have forgotten this by dinner time that same evening. :-( His highlights list shouldn't take a "You-must-include-this-info" tone but should instead be more along the lines of "I thought it might help you to have these reminders right in front of you."