A six-hour aptitude test battery was constructed as an aid to better understanding of course grades. The test had 20 separately timed parts. The parts were designed to test aptitudes that might be needed for many courses. Entering freshmen at the United States Coast Guard Academy (USCGA) were given the battery. Data are available for 105 cadets. It was also given to Boston University General College (BUGC) students in May, 1948. Data are available for 241 students in one division and 298 students in another. Separate scores were obtained for parts of course grades. They were correlated with each other and aptitude test scores. Marks of students for homework, class tests, recitation, portions of mid-term and final exams, and term papers were obtained. The six parts of the aptitude battery are: 1) spatial; 2) social studies; 3) algebraic symbols; 4) speed of computation; 5) common sense science; and 6) vocabulary. Intercorrelations of course grades and test scores for the USCGA are shown in Table 1. Tables 2 and 3 show the intercorrelations of course grades and test scores for BUGC students. (SGK).