My experience is it is the the top kids who are spending the most money & time on test prep. Elite 4-5 hours a day all summer long test prep is a BIG thing for the 'highly motivated' straight A top students in my area. These students can change their scores by 40-100 or so points withe enough practice. And if your changing from a 1480 to a 1550 (out of 1600) can make a difference to elite college admissions. Particularly if you are from an ethnic makeup where you are discriminated against.
On the other hand I've heard these elite test prep centers usually give them false low scores on their first "sample" test so it looks like their improvements are greater than they are. And yes these test centers are very rigid study experiences. Lots and lots of repetition of the same material over & over again.
On the other hand I do believe that some test prep can be helpful and make a small amount of difference. Had my DS take a sample SAT cold and he overthought many of the math questions.
