It is a measure of demonstrated Math and Verbal skills. These skills can be learned. SAT content is limited. Learn the range of the content areas and your preparation becomes focused and easier. SAT scoring is predictable .
Standardized tests measure all students against the same standard.
On the SAT, this means that if you take the test in November, you are measured against the students who took the test in June. Of course you aren't taking the SAME test they took. The SAT is an opportunity. Colleges use the SAT as a common yardstick by which to measure candidates. With adequate preparation, it really isn't hard to do.