I'm a current Columbia SEAS student (class of '14) and I'm working on starting a company that provides application and essay counseling/advice, but I'm trying to freelance my services a bit before diving in. I'm planning on offering one on one skype conferences to evaluate candidates' essays or applications/supplements. Contact me at firstname.lastname@example.org
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In response to your question, I had a 780 chem and was accepted, but that's above the average score (middle 50%) for Columbia. In general, a school's SAT II average should be similar to the SAT average (low to mid 700's for Columbia). You should be fine.