Understanding what factors foster young people's aspirations to work as teachers is critical for designing effective recruitment policies, and for ensuring that enough youngsters enter the teaching profession. We examine what factors explain between-country differences in the percentage of 15-year-old students who expect to work as teachers as adults. We focus on two factors: (1) the salaries teachers can expect to earn compared to professionals in science, technology, engineering and mathematics (STEM); and (2) the skill levels teachers have compared to STEM professionals. Relative salaries indicate if (and to what extent) the financial returns associated with teaching careers are higher or lower than professional STEM careers dominated by men. Relative skills highlight the investment in human capital that teachers are expected to make to be able to enter the profession, as well as the social and cultural status that is associated with teaching. We used data from 29 countries that participated in the Programme for International Student Assessment and the Programme for International Assessment of Adult Competencies. In countries where teacher salaries and numeracy skills were high compared to those commanded by STEM professionals, gender gaps in teaching career expectations were smaller. High-ability students in science and mathematics were more likely to expect to work as teachers in countries where teachers have comparatively higher numeracy skills. Our findings show that when teacher salaries are competitive in relationship to the salaries of STEM professionals, more students overall expect to work as teachers. However, whilst low- and middle-performing students in science and mathematics were attracted by economic incentives, high-performing students in science and mathematics were not.