The SAT goes from 200 - 800. If test prep raises average score by 100 points, there still is some room for the test to show actual knowledge.

The college board says that an SAT is better predictor of success in college than GPA, which based on my experience of American high schools makes sense. I get that wealth probably has a positive correlation to both. But it seems that should matter a little.

Why do you exclude learning the material as a reason? My test prep was largely a matter of learning material that I missed or wasn't taught effectively during school.

I would group that under familiarity with test content. Maybe an opaque label on my part.

although? Or the most important factor is, quality of prep. A man/women who have continuously, kept practicing to improve academically, becomes insignificant. However, keep throwing ball in hoop would help math and science innovations. This is absolutely insane.

Is this just personal anecdata?

An acquaintance of mine runs a high end SAT training program. He gets these results reliably for folks who have had little or no preparation before coming to him. Trained test takes is in the hundreds (maybe more).

Is this data or anecdata? You be the judge. He finds it easy to bank on professionally.

I encourage you to talk to someone who has worked at a high-end SAT training program (not Kaplan or that type). They can tell you the real deal, both successes and failures. Don’t rely on talking to the businesses themselves, because they will be selling their services rather than telling the complete truth (unless you know them personally).

Fwiw, failures are usually due to one of a few factors:

1. anxiety

2. learning blocks

3. physical issues (e.g., lack of sleep, sick, etc.).