Out-of-field mathematics teaching and its impact on student achievement across countries: evidence from TIMSS 2023

Abstract Although assumptions regarding out-of-field (OOF) mathematics teachers—such as their limited knowledge, motivation, or self-efficacy—are often linked to a negative influence on student achievement, empirical evidence in this regard remains inconsistent. Using TIMSS 2023 data from eighth-grade students, this study applied a Bayesian multilevel modeling framework to analyze cross-country patterns in the relationship between OOF teaching and mathematics achievement among students. The analysis included country-specific models alongside an overall international model with country fixed effects. The results revealed that, in the overall international sample, students taught by OOF teachers scored, on average, 7.7 points lower in mathematics than those taught by in-field teachers. This negative association remained consistent across all content and cognitive domains in mathematics. However, country-specific models revealed substantial variation: Finland—where 24.9% of eighth-grade students are taught OOF in mathematics—demonstrated a clear negative association, with students taught by OOF teachers scoring, on average, 14.1 points lower than those taught by in-field teachers. Overall, the global effect of OOF teaching appears relatively modest, with persistent negative impacts observed in only a subset of countries. These cross-national differences suggest that contextual factors—such as professional development opportunities and institutional support—may help offset potential disadvantages of OOF teaching.