The objective of this study was to evaluate the performance of students of college of Science of Sultan Qaboos University (SQU) in Calculus I course, and examine the predictive validity of student's high school performance and gender for Calculus I success. The data for the study was extracted from students' database maintained by the Deanship of Admission and Registration office of SQU. The study considered a sample of 615 students who took Calculus I course during 2014 spring semester. Both descriptive and inferential statistical techniques were used for data analysis. Predictive validity of selected factors were analyzed using Hierarchical regression analysis. The analysis revealed that female students entered in SQU with a higher average high school scores than male students, and many boys with lesser high school scores than girls were succeeded in getting admission at SQU. The results indicate that female students outperformed male students in both high school and college Calculus course. About 30% of the students obtained grades lower than C in Calculus I, of which 20% failed in the course. The proportion of students with F grade was found to be significantly higher among male students compared to female students (28% vs. 7%). The analysis revealed that gender, high school math score and overall high school score are significant predictors of subsequent performance in Calculus course at college level. Thus differences among gender and high school performance should be taken into consideration during the admission process to allow for more equal opportunities to all applicants and have fairer admission decisions.