To compare 'in-field' versus 'out-of-field' teachers of Years 7-10 mathematics in Australia on key demographic and instructional dimensions, we analysed nationally representative system data collected by the OECD Teaching and Learning International Survey (TALIS), one of the world's largest survey of teachers and school leaders. Latest available TALIS 2018 data from teachers teaching Years 7-10 mathematics (N = 1,120; 284 of whom taught mathematics out-of-field) showed out-of-field teachers were mostly from a STEM background qualified to teach science and/or technology, and were less commonly older or more experienced. Out-of-field teachers were more concentrated in public schools, having less principal autonomy, lower academic pressure, with greater school delinquency and violence. There were no statistically significant differences between in-field and out-of-field teachers on their non-mathematics specific motivations, values, self-efficacy, professional development needs and barriers, professional engagement or wellbeing. Specific to mathematics teaching, we compared 'in-field' versus 'out-of-field' Years 7-10 mathematics teacher reports of key instructional practices specific to a 'target' mathematics class (N = 472; 65 of whom taught mathematics out-of-field), which revealed likely negative consequences for student engagement and learning. Out-of-field teachers spent more time than in-field teachers on classroom management and disciplining students, lost more time due to student interruption, reported much disruptive noise in class, only occasionally presented tasks for which there was no obvious solution, and spent less time teaching, although they did not differ on time spent in practices related to instructional clarity. Out-of-field teachers also reported more time setting students extended projects to complete, letting students evaluate their own progress, and providing immediate feedback when observing students working on particular tasks. Targeted mathematics classes taught by out-of-field teachers had higher concentrations of low-achievers, indicating a bias in which students are assigned teachers not specialised to teach mathematics. Recommendations are advanced regarding professional development priorities for teachers teaching mathematics out-of-field.
