BackgroundAchievement tests are designed as measurement tools for student knowledge and learning, but also reflect student effort during the test. Understanding better what determines differences in (different dimensions of) effort can help in understanding what measured achievement differences reflect. AimWe analyze how test-taking effort relates to students’ demographic characteristics, past attainment and personality traits. Data13,791 9th grade students in the Netherlands, administered in 2012, 2014 and 2016, answering a total of 449,956 observations. MethodsWe distinguish between two measures of effort: solution behavior and response time given solution behavior. We estimate multi-level cross-classified models that include individual and test characteristics as predictors. We further include interaction terms between question position and individual characteristics, to identify how effort decline across the test differs by student type. ResultsGirls, high achievers, more agreeable, more conscientious and less extravert students exert more effort. Differences by past achievement are especially large and further increase along the test, while differences in other characteristics tend to be more stable. Effort differences by socioeconomic status are relatively small. ConclusionsSystematic differences between different types of students can partly reflect differences in test effort across these groups. Thus, test effort should be considered when analyzing achievement gaps and differences across learning outcomes. Tests with different test lengths imply different measures of educational inequality through differential effort declines.