What is in a Score or Grade?

It is that time of the year. Some students are taking standardized exams and it is near the end of a school year so students are about to receive their final grades. Getting admitted to a college depends on these two so it is important to know what information one really gets from a student's score in a standardized test and from a student's grade point average (GPA). These two measures are already known to correlate with a student's graduation rate from college. This can be seen from a graph drawn by Preston Cooper in Forbes Magazine based on data presented in a study by Matthew Chingos.

Above copied from
Preston Cooper, Forbes magazine. "What Predicts College Completion? High School GPA Beats SAT Score"

From the above graph, it is clear that high school GPA is a much more discriminating tool and is a better predictor than scores in a standardized test when it comes to success in college. Except for the fact that students who score less than 800 are sharply less likely to finish college, there is not much difference among students who score above this threshold. As someone who has worked on composing standardized tests, I know that a standardized exam can be a very useful tool in identifying deficiencies or problems, but not in predicting degree of success, so this finding is not surprising. It comes with the nature or inherent limitation of questions one could fairly ask in a standardized test. High school grades, on the other hand, are much wider in scope, both in content and time. A student's grade does not depend solely on a one-time one or two-hour performance, but on an entire semester or year. And recent work by Galla and others has been able to extract the various factors contributing to high school grades and standardized test scores. For GPA's they find the following:

Above copied from
Galla, B. M., Shulman, E. P., Plummer, B. D., Gardner, M., Hutt, S. J., Goyer, J. P., … Duckworth, A. L. (2019). Why High School Grades Are Better Predictors of On-Time College Graduation Than Are Admissions Test Scores: The Roles of Self-Regulation and Cognitive Ability. American Educational Research Journal. https://doi.org/10.3102/0002831219843292

Self-regulation, the most important factor in a student's GPA, includes self-control, primarily the ability to delay self-gratification in order to meet longer term goals. It is therefore not surprising why GPAs better correlate with success in college since higher education requires a lot more independence than basic education does. 

For scores in standardized tests, these are the factors Galla and coworkers find:

Above copied from
Galla, B. M., Shulman, E. P., Plummer, B. D., Gardner, M., Hutt, S. J., Goyer, J. P., … Duckworth, A. L. (2019). Why High School Grades Are Better Predictors of On-Time College Graduation Than Are Admissions Test Scores: The Roles of Self-Regulation and Cognitive Ability. American Educational Research Journal. https://doi.org/10.3102/0002831219843292

Scores in a standardized test measure something different. The biggest factor is cognitive ability. It depends mainly on intelligence. It does not measure effort or persistence. 

Obviously, the above do not tell us everything about a student. College admissions cannot and should not value one over the other nor should they consider only test scores and grades. GPAs will lose their predictive power with grade inflation and standardized test scores will become useless if these tests are compromised. Nonetheless, it is important to take note of the difference in information, a score in a standardized test, or a grade in a report card actually provides.