The purpose of the current study is to investigate the feasibility of accounting for student performance in advanced high school coursework through the adjustment of high school grade point average (HSGPA) while separating out variables that are independently considered in the admission process, e.g., SAT/ACT scores, community affluence, type of high school, and race/ethnicity. This study relates three variables: high school science grade, high school course level (i.e., regular, honors, Advanced Placement (AP), and AP examination score. These three are compared, using as a common metric how well students perform in their introductory college biology, chemistry, or physics coursework. The authors collected data from more than 18,000 students at 63 randomly selected colleges and universities stratified by size to match the proportional enrollment at small (enrollment less than 1,000 students), medium, and large (enrollment greater than 10,000 students) institutions. For the purposes of their analysis, the authors limited their sample to first-semester, introductory biology, chemistry, and physics courses fulfilling graduation requirements for science or engineering majors. Two variables were found to correspond to substantially better performance in college science courses: increasing rigor of high school science experience and higher grades in high school science courses. These two variables can be related to each other using relative improvement in college grade as a common metric. The results are stable even with the inclusion of control variables--variables typically treated separately in the admissions process. In units of high school letter grade, an honors course in the subject corresponds to an increase of one-half of a letter grade and an AP courses corresponds to an increase of one letter grade; for students who pass the requisite AP exam, the grade level equivalent is two additional letter grades. (Contains 3 figures, 2 tables and 6 footnotes.)