To better understand the library's role in student success, this research used student survey data to explore students' reported library building use, library resource use, library instruction, as well as student perceptions of the library's role in their success, and how these factors may vary by academic discipline. Cumulative GPAs were also matched with respondents. Quantifying the relationship between library usage and student success is one of the six areas recommended for further research by ACRL. This study focuses on the variation and the uncertainty of the measurement of this relationship across disciplines, using Bayesian multilevel regression methods. Levels of library resource usage and percentages of respondents believing the library contributes very much to the respondents' academic success vary quite a bit by discipline. In this study, cumulative GPA is higher on average for students who use library resources more frequently, but not for students who receive library instruction. Although, for undergraduates, higher frequency of building usage predicted higher probability of believing the library contributes very much to academic success, it did not predict higher GPA.