The value of teacher professional development (PD) is widely acknowledged. However, limited research has been done on the impact of PD on classroom practice in the post-intervention classroom. This chapter provides an overview of a funded project involving natural science teachers in South Africa. The PD intervention included a three-day short learning programme (SLP) on the infusion of indigenous knowledge in curriculum themes. The design-based, mixed-methods research focused on teachers’ self-directed learning (SDL) as a foundation for teacher PD in order to future-proof teacher education. Data were collected by means of classroom visits, evidence-based portfolios, completed SDL instruments, and interviews with selected teachers. The findings showed that, with exceptions, a wash-out effect occurred and many teachers reverted to transmission-mode pedagogies after the intervention. Teachers’ PD was also mapped utilising a revised Profile of Implementation heuristic. The findings demonstrated that SDL is essential to PD. Third-generation Cultural-Historical Activity Theory (CHAT) was used as a heuristic with which the findings were explained. Several tensions were identified relating to the lack of transfer of reformed teaching practices. Based on these findings, it is proposed that systemic approaches should be followed when planning and engaging in PD programmes. The value of Change Laboratories and fourth-generation CHAT is also discussed.