What teachers' think about student engagement influences the teaching practices they adopt, their responses to students and the efforts they make in the classroom. Interviews were conducted with 31 mathematics teachers from ten high schools to investigate their perceptions and beliefs about student engagement in mathematics. Teachers also reported the practices they used to engage their students during mathematics lessons. Teacher perceptions of student engagement were categorised according to recognised "types" (behavioural, emotional and cognitive) and "levels" (ranging from disengaged to engaged). The teachers' reports emphasised immediate attention being paid to students' behaviours and overt emotions towards mathematics with fewer and less extensive reports made about students' cognitive engagement. Teachers' abilities to implement practices considered supportive of student engagement were linked to a number of elements, including their self-efficacy. Perceptions of being powerless to engage their students resulted in many teachers limiting their efforts to attempt some form of intervention.