Universities and colleges at the Kingdom of Saudi Arabia assess new applicants using academic indicators, such as high school grade point average (HSGPA) and the score of a national standardized test (the General Aptitude Test), to ensure that they are academically fit to join the institution. Such criteria have been suggested in previous research as true predictors of students' competences (AlQataee & Al-Harbi, 2012). In addition, admitted students are required to complete one full academic year of preparatory courses. However, many students who join Prince Sultan University--a private university in the Kingdom--struggle to complete mathematics courses assigned in the preparatory year, although most of them have achieved high HSGPA and high score in the standardized test. The reported study looked at the prediction relationship of three explanatory variables: HSGPA, the General Aptitude Test (GAT) score and Gender, and the GPA of preparatory year mathematics courses (dependent variable). The findings indicated that nearly 34% of the variation in the dependent variable is explained by HSGPA, GAT and Gender. The regression model found to be significant. However, future research is needed to examine other factors that might be behind students' struggle in mathematics courses.