Academic intensity or academic rigor of students' high school curriculum is positively related to several college outcomes including the avoidance of remediation and graduation attainment. However, research on academic rigor has been limited possibly due to the difficulty in obtaining a quantitative measure applicable across schools and districts. This study is an attempt to create an index of academic rigor using self-reported course work data that would assist in providing information on the academic preparation of over one million graduating high school seniors each year. The current study uses the SAT® Questionnaire (SAT-Q) that students complete when registering for the SAT exam to construct an academic rigor index (ARI). The SAT-Q asks students detailed questions on English, math, science, social science/history, and foreign/ classical language course work completed during high school. The relationship between course participation and first-year GPA (FYGPA) was investigated using approximately 68,000 SAT takers students who fully completed the SAT-Q and attended one of the 110 four-year colleges and universities participating in an SAT validity study. Based on this data, the ARI was constructed on a 0-25 scale equally weighted between each of the five subject areas. Once the ARI was constructed a series of analyses were conducted to assess the relationship between the index and other concurrent measures of high school performance (HSGPA and SAT scores) and between the index and measures of college performance (enrollment, grades, and retention). The results indicated that students who took more rigorous courses in high school attained better grades, achieved higher SAT scores, and were more likely to enroll in college. Moreover, these students were also more likely to matriculate to a four-year college, attain higher college grades, and be retained to their second year. A questionnaire, English scale, and tables are appended.