From a three-year study by the National Association for College Admissions Counseling that showed grades—not SAT or ACT scores—are the best predictor of college success:
College and university cumulative GPAs closely track high school GPAs, despite wide variations in testing. Students with strong HSGPAs generally perform well in college, despite modest or low testing. In contrast, students with weak HSGPAs earn lower college cumulative GPAs and graduate at lower rates, even with markedly stronger testing. A clear message: hard work and good grades in high school matter, and they matter a lot.