Low motivation to perform well on a test is a potentially problematic source of construct-irrelevant variance (Messick, 1980), especially when there are low or no stakes attached to performance. That is, interpretations of test scores as indicators of students' knowledge and skills may be compromised if those students do not put forth the effort necessary to demonstrate the full extent of their abilities. High motivation has been reported in some international testing contexts (Baumert & Demmrich, 2001; Eklöf, 2007), owing to factors including social responsibility, competitive spirit, interest, and personal or intrinsic motivators (Eklöf, 2008). Such findings sharply contrast with U.S. students taking low-stakes tests like NAEP where a large percentage of students report a low sense of importance and low effort (ETS, 1993). This study investigates two cohorts of students and the possible associations with effort and performance on CLA+, an international assessment of college students' critical-thinking and writing skills. The first cohort was administered the assessment in a low-stakes condition where student performance was not associated with any outcomes. The second cohort was administered the assessment in a high-stakes condition where the students' CLA+ results would be used in conjunction with other criteria (e.g., GPA) to decide on their placement into a post-university program.