<p>Coming from an American education system, you will find it VERY, VERY difficult to sit an A-level. Students prepare for those by taking GCSEs (in 11ish subjects for normal unis) three years before, and then AS-levels the year before, and then A-levels. As has been mentioned, they are very much more difficult than APs. I did indeed read on one of the C'bridge college sites that 4 5's and one 4 in AP should be attained before an application was considered, as another poster mentioned. </p>
<p>Oxford (at least) does not accept transfers for undergrad. So, if your SAT score was on the 1600 scale, have you already started uni?</p>