Typical Intellectual Engagement (TIE) is considered a key trait in explaining individual differences in educational achievement in advanced academic or professional settings. Research in secondary education, however, has focused on cognitive and conative factors rather than personality. In the present large-scale study, we investigated the relation between TIE and achievement tests in math and science in Grade 9. A three-dimensional model (reading, contemplation, intellectual curiosity) provided high theoretical plausibility and satisfactory model fit. We quantified the predictive power of TIE with hierarchical regression models. After controlling for gender, migration background, and socioeconomic status, TIE contributed substantially to the explanation of math and science achievement. However, this effect almost disappeared after fluid intelligence and interest were added into the model. Thus,we found only limited support for the significance of TIE on educational achievement, at least for subjects more strongly relying on fluid abilities such as math and science.