Because so many students at the top universities have great ACT or SAT scores, I do recommend that students *consider* Subject Tests. You’ll only want to worry about them if you think that they can improve your testing portfolio. In the case of elite schools like Columbia, that means 750+ (or at least 700+). You can try tests from the Official Guide published by College Board. Fewer schools than ever are requiring the Subject Tests — especially with ACT scores. It would be a little challenging to fit them in (including preparing for them) as senior year starts and application season begins, so you may want to just sit tight with your ACT score.
New applicants should exercise discretion when responding to this prompt, as providing an optional essay creates extra work for the admissions reader. This will be a good place to address extenuating circumstances that have influenced one’s academic or professional history, to address weaknesses in one’s application, or to explain an unusual choice of recommender. The wording of this question is open enough that applicants may also choose to discuss an element of their background that is not reflected in their other materials (including data forms and résumé), though they will need to demonstrate sound judgment in doing so – . the nature of the content should be such that it makes a material difference to one’s application – and should summarize the information as concisely as possible.