Originally Posted by Val
Sure, people with (near) perfect scores on the SAT have aptitude for college work, but they aren't the only ones. Plus, given the way the test is scored, it isn't clear to me that anyone can even honestly discriminate between "aptitude" in students with scores between ~650 and 800.
The relationship between PSAT scores (and very likely SAT scores) and college grades is close to linear throughout the range of PSAT scores.

Examining the Linearity of the PSAT/NMSQTFYGPA Relationship
By Jessica P. Marini, Krista D. Mattern, and Emily J. Shaw
Executive Summary
There is a common misperception that test scores do not predict above a minimum threshold
(Sackett, Borneman, & Connelly, 2008). That is, test scores may be useful for identifying
students with very low levels of ability; however, higher scores are considered unrelated to
higher performance for those above a certain threshold. This study aims to examine whether
this is true for the Preliminary SAT/National Merit Scholarship Qualifying Test (PSAT/NMSQT),
which is used for that very purpose to differentiate among very high performing students.
The linearity of the relationship between PSAT/NMSQT scores and first-year college GPA
(FYGPA) was explored in this paper, using a regression approach. This relationship was
explored over the entire range of the PSAT/NMSQT score scale, known as the Selection
Index, ranging from 60 to 240 as well as the upper end of the score scale (≥ 200), where
initial screening decisions are made for scholarship programs conducted by National Merit
Scholarship Corporation (NMSC). For the full PSAT/NMSQT scale, the addition of a quadratic
term improved model fit; however, the effect size was small as indexed by the change in the
squared multiple correlation coefficient (R2
) of 0.001. That is, including PSAT/NMSQT Selection
in the model accounted for an additional 0.1% of variance in FYGPA. As for the subset
of students who had a PSAT/NMSQT score of 200 or higher, the results indicated a strong
linear relationship, which suggests that even among very high-scoring students, the PSAT/
NMSQT score scale differentiates between students in terms of academic success measured
by grades earned in the first year of college. In sum, the results of this study support the use
of the PSAT/NMSQT as a screening tool for selecting Merit Scholarship winners.