^^^^Completely agree. In the dark ages when I was taking the SAT, I scored ‘ok’ on the first try. Then, went through Kaplan for 8 weeks. Improved slightly. My saving grace was superscore of the ACT.
Fast forward to my DSx3. It was different for all three. They used a combination of practice tests and online tutoring as needed. For my twins, one studied a ton - 1550. His brother barely cracked the study guide - 1510. The only solid answer is - it depends on the kid and their (not your) goals.