The problematic persistence rates that many colleges and schools of engineering encounter has resulted in ongoing conversations about academic readiness, retention, and degree completion within engineering programs. Although a large research base exists about student preparedness in engineering, many studies report a wide variety of factors that makes it difficult to address specific issues that prohibit students from completing a degree in engineering. Many studies anecdotally address mathematics achievement as a factor associated with success, but few contain empirical data specifically related to success or readiness to take calculus. This study specifically examines engineering degree completion of calculus eligible students compared to non-eligible calculus students upon acceptance into a College of Engineering as a first-semester freshman, and the mediating effects of being at-risk for non-matriculation on this relationship. A 10-year span of engineering student data, including admission and completion data, was accessed and analyzed to investigate student preparedness (as defined by calculus eligibility) and student success (as defined by at-risk status for non-matriculation) as they related to graduation rate. This study documents a partial mediating effect of at-risk status on the relationship between calculus eligibility and graduation rate; however, calculus eligibility remains a significant predictor of graduation rate and together with at-risk status predicts a significant proportion of the variance in graduation rate.