Two prospective surveys tested theory-based models of university students' study behavior and grade point average (GPA). The theory of planned behavior (TPB) and personality systems interaction (PSI) theory were tested. The TPB fitted the data for self-reported study but was less useful when applied to GPA. Some support for PSI theory was found although results varied for study behavior verses GPA. In Study 1, an interaction between volitional competency and subjective norm explained unique variation in study behavior controlling for TPB variables and past behavior. In Study 2, implicit attention control had a direct effect on GPA after the TPB variables and past achievement were controlled. Implications for interventions designed to improve tertiary-level academic achievement are discussed.