Out-of-field (OOF) teaching remains a common practice in secondary schools, particularly in mathematics where teacher shortages are prevalent. Surveys of school leaders ( $N=100$ ) and mathematics teachers ( $N=217$ ; of whom 97 OOF) from 48 Australian government schools explore: 1) difficulties schools leaders experience to employ qualified mathematics teachers; 2) leaders’ preferences for assigning OOF teachers to classes, comparing Principals/Deputies and Head Teachers; 3) the characteristics of OOF mathematics teachers and their reasons for teaching OOF; and 4) potential consequences of teachers teaching mathematics OOF—for themselves and the students they teach. Leaders’ preference to address shortages was recruiting retired teachers followed by sharing programs between schools. Principals/Deputies preferred requiring teachers who had availability to teach mathematics OOF, which Head Teachers wished to avoid. Both groups preferred assigning teachers skilled in mathematics, who valued mathematics more, experienced and skilled pedagogues who coped well with demands and were willing, and wished to avoid early-career teachers. Both leader groups preferred allocating OOF teachers to junior secondary classes, to students who had average mathematics achievement and motivation. OOF teaching was most concentrated in grades 7-8, then grades 9-10; over one-third taught grades 11-12 but typically not advanced levels. OOF teachers had less teaching experience than infield; most had advanced grade 12 as their highest mathematical background. OOF teachers reported positive reasons for teaching mathematics, but also experienced anxiety. They were less confident than infield teachers across all junior secondary mathematics topics. Infield and OOF teachers reported similar levels of student engagement, but OOF teachers used fewer deep learning strategies. Implications for policy and mathematics teaching and learning are advanced.
