School leaders employ various school-based actions to influence students' subject enrolments at senior secondary levels (Years 11 and 12), which in turn affect students' entrance into tertiary courses and career choices. In the context of reported declines in the proportion of students opting to study higher-level mathematics, this qualitative study sought insights into seven Australian mathematics teacher leaders' decision-making processes and actions in their particular school contexts. It aimed to relate their actions to particular attributions for enrolment declines and their goals for students' learning and achievement. The leaders' attributions included students' lack of ability, changes in university courses' pre-requisites, students' lack of effort or persistence, and negative attitudes towards mathematics. The leaders described a variety of school-based actions; some school leaders had actually chosen opposing actions but expressed similar reasons for implementing them, and vice versa. Tensions among external pragmatic constraints, the actions of other school staff, and the teacher leaders' own goals for student learning in mathematics framed the findings of this study.