Examining textbook effects in primary mathematics: The moderating role of teachers’ professional knowledge

Mathematics textbooks are central resources in the classroom, yet research on their impact on student learning outcomes remains limited. This study analyzes textbook effects on grade 2 mathematics achievement and tests whether teachers’ professional knowledge moderates these effects. Data from 1134 students nested within 63 classes using four widely used textbook series in Germany were analyzed using multilevel random intercept models, controlling for prior achievement and teaching quality. Results indicated significant differences in student achievement across textbooks, with some series yielding higher achievement than the reference textbook. Teachers’ professional knowledge can moderate these effects: textbook effects were higher at lower levels of teachers’ professional knowledge and diminished at higher knowledge levels for some textbooks. These findings indicate that textbook effects depend on both the materials used and teacher expertise, highlighting the need for research on underlying mechanisms as well as for evidence-based textbook selection and targeted teacher professional development.