GMAT vs SAT
The GMAT is a much more complex test, with questions that cover a broader range of topics. The questions on the GMAT are also much more difficult to answer than the questions that are found on the SAT.
Scoring also varies between the two tests. Though both tests use the 200 to 800 scale, most people find that their GMAT scores are much lower than the scores that they received on the SAT.