A diagnostic test for assessing the general and Earth science knowledge of entry-level college students was administered to 451 students in 2002 and 401 students in 2003 enrolled in an introductory geology course at Iowa State University. The study shows that male students, seniors, and science-technology-math majors score higher than female students, freshmen, and non-science-technology-math majors and that the differences are statistically significant. Also, students who scored higher on the diagnostic test were more likely to pass the course. The results support the feasibility of a standardized diagnostic test as a tool for geoscience instructors for curriculum planning, student advising, and curriculum assessment, similar to standardized diagnostic testing and pre-post testing used in chemistry and physics courses. Standardized national tests would enhance college geoscience education.