The present study focuses on forty out-of-field teachers who have been teaching science for a few years in primary or lower-secondary schools and entered a two-year professional development programme to qualify as in-field teachers. Our purpose was to uncover their reasons for teaching science without appropriate qualifications, their motivations to enrol in the programme, and the extent to which the programme enhanced their competencies as science teachers. Findings revealed two motivational profiles: an intrinsic one and a mixed one that combined intrinsic and extrinsic orientations. All the teachers admitted they had lacked the content knowledge and the pedagogical content knowledge required to teach science effectively. The programme contributed mainly to their disciplinary and pedagogical knowledge and to their self-efficacy. While some positive aspects of out-of-field teaching came up, measures should be taken to ensure that the limited knowledge of out-of-field teachers does not affect the quality of their teaching.