<p>there are a lot of differences between the SAT and ACT which could cause a person to score better on one test versus the other one The ACT has a science reasoning test that is not on the SAT. The ACT has no guessing penalty for wrong answers, but requires the test taker to work more quickly and budget time for longer sections. The ACT covers trig which is not covered on the SAT. That’s just a few differences. I am not sure how they come up with the SAT/ACT concordance- I think it is based upon percentile results rather than the results of individual test takers. It may be that the SAT score, say, that puts a person in the 90% percentile of SAT takers is equated to the ACT score that puts a person in the 90% percentile of ACT.</p>