<p>Admission to Oxford or Cambridge is tough for a U.S. student fresh out of High School. You can improve your chances significantly though if you apply after completing one year of college-level education in the States. Note however that you won’t be considered as a transfer student in that latter case; instead, you will still have to apply and be admitted as a freshman. </p>
<p>In any case, if you decide to apply to Oxford or Cambridge, in addition to a solid GPA and good SAT scores, admission tutors probably will be expecting you to have taken four or five AP exams, with a 5-5-4 score or higher in 3 subjects that are considered directly relevant to your intended major. You may also have to go through an oral interview during which you may be required to take additional reasoning tests and/or answer questions of a technical nature. Depending on your prospective major, those can be for example math/physics problems or questions about a previously unseen passage/text you will be asked to read prior to the interview.</p>