The basic test is the SAT 1, which measures maths and verbal reasoning in a three-hour, multiple-choice test. The maximum score is 1,600, with candidates given a separate score of 200-800 for the two sections. 1,200 is about the minimum required for entry to a top US university, although Harvard would expect more than 1,400.
Many US colleges also require candidates to take one or more SAT 2 tests, which are one-hour tests in 22 subjects such as science and foreign languages.
In the South and Midwest, the ACT, another college admission test, is more popular. Taken by about 1.2m high school students a year, it is curriculum-based, and measures students' ability in English, maths and science. Maximum score is 36.
Just as Britain considers introducing the SAT 1, or something like it, the American test is about to change radically. This follows criticisms that it distorts the curriculum, promotes coaching and favours the middle class - and a threat to stop using it by the huge University of California.
For college entry in 2006, US high school graduates will sit a test that includes more advanced maths and an essay. The SAT will no longer be all multiple choice; candidates will have to show they can write. A bit more like A-levels, you could say.