The SAT exam is an aptitude test which affects all university/college applications. All universities compare applicants on SAT scores but some have strict requirements. SAT exams consist of three main areas; critical reading, maths and writing. Subject SAT exams can also be taken to add weight to a degree application and may be required for certain bachelor degrees. The average SAT score required for each degree varies, but esteemed universities or difficult courses require higher scores (for example, Harvard University requires a score in all areas of 680 - 800, which is 20 percent above the average student score of 500).
Not all institutions will accept applicants solely on SAT scores. ACT (American College Test) exams are an alternative to SAT scores or they can be taken in addition to the SAT. They are knowledge-based exams which test the achievements of a student and what students have learnt throughout their education. ACT requirements vary again for each institution and can be submitted in conjunction with SAT scores or without. Some institutions will require GPA (grade point average) scores along with SAT and ACT scores. GPA scores reflect the average grade throughout education (for example, a score of 4.0 is an "A", 3.0 is a "B" and so on until 0.0 which is a fail.) Again, institutions have various requirements for GPA scores and some may not even require GPA scores at all.
United States universities may request international students to take a TOEFL (test of English as a foreign language) exam before being accepted into the institution. It is not uncommon for universities to request one year of independent study in the United States. The minimum score accepted by most universities is 500 but, again, the criteria vary for each university.
Prestigious institutions will not base their decisions solely on exam scores and may request additional tests to be taken by applicants. Exams are normally written and test the applicant's analytical ability as well as their essay writing/prose skills. For specialized courses, some institutions may offer a knowledge based exam on the subject, or simply request additional learning before applying for a bachelors degree (such as a two year associate degree).
Although extracurricular activities and AP (Advanced Placement) classes are not a specific requirement for all universities, they normally give extra weight to an application. Activities that are centered around the subject which the student will study at degree level are appealing to institutions --- AP classes, in turn, are challenging courses that can be taken before university and are recorded on a student's record. Students studying advanced placement courses gain a distinct advantage in academic writing, research and financial planning and they gain a distinct advantage over other potential students.