The primary determinant of a student's admission score line for high school in the United States is a combination of their Grade Point Average (GPA) and standardized test scores, such as the SAT or ACT. The average GPA for high school admission to competitive colleges and universities is typically around 3.5 to 4.0 on a 4.0 scale. However, this can vary widely depending on the institution and the student's intended major. For example, top-tier universities like Harvard and Stanford often require GPAs above 4.0, while state universities may accept a GPA as low as 3.0.

Standardized test scores also play a crucial role. The average SAT score for admission to competitive colleges is around 1300-1400 (out of 1600), and the average ACT score is around 28-32 (out of 36). However, these scores can be significantly higher for students applying to highly selective institutions. For instance, the median SAT score for admission to Harvard is around 1550, and the median ACT score is around 34.

The reason for these score lines is rooted in the competitive nature of college admissions in the United States. With a high number of qualified applicants, colleges use GPA and standardized test scores as objective measures to evaluate candidates. Data from the National Center for Education Statistics (NCES) shows that the average GPA for students admitted to four-year colleges in 2019 was 3.34, and the average SAT score was 1050. These figures highlight the importance of achieving strong academic performance and test scores in the admissions process.

Moreover, the COVID-19 pandemic has led to changes in the admissions landscape, with many colleges adopting test-optional policies. This means that they no longer require standardized test scores for admission, allowing students to showcase their academic abilities through other means, such as GPA, extracurricular activities, and personal essays. However, even with these changes, a strong GPA and a competitive test score can still significantly enhance a student's chances of admission to their desired institution.