I just looked this up and apparently we are both wrong hehe. I guess the R-square is 0.4 for LSAT-1L grades. But we are right in the fact that the LSAT is more strongly correlated than GPA.
""There is a controversy over the statistical correlation between LSAT score and first year law school grades. LSAC claims that their own research supports the use of the LSAT as a major factor in admissions, saying the median validity for LSAT alone is .41 (2001) and .40 (2002) in regards to the first year of law school.[7] Although the correlation varies from school to school, LSAC claims that test scores are far more strongly correlated to first year law school performance than undergraduate GPA.[8] LSAC claims that no more strongly correlated single-factor measure is currently known, that GPA is difficult to use because it is influenced by the school and the courses taken by the student, and that the LSAT can serve as a yardstick of student ability because it is statistically normed. Several outside studies have validated that the LSAT is a valid predictor of both Law School Grades as well as bar passage.[9][10][11]"
Law School Admission Test - Wikipedia, the free encyclopedia