Abstract

Teacher professional development (TPD) programs should address individual knowledge gaps and diverse prior knowledge among participants. E-learning formats have emerged as promising solutions, offering flexibility and accessibility tailored to teachers' needs. While these programs enhance access, ensuring quality experiences and outcomes remains challenging. The study reported in this article analyses the effectiveness of a course within an online teacher professional development program designed to enhance mathematical knowledge for teaching numbers and operations to primary school teachers in Chile. The program aims to develop teachers' mathematical knowledge for teaching (MKT) through contextualised learning activities. A quasi-experimental design was employed to assess the program's effectiveness in improving the MKT of teachers with different specialisation backgrounds. The performance results of the MKT of 99 teachers, both with and without specialisation in mathematics, were analysed before, during, and after participation in the program. The results reveal significant gains in MKT across all participants, regardless of initial MKT levels or specialisation backgrounds, underscoring the inclusivity and efficacy of the systematically designed course. These findings highlight the potential of such structured professional development initiatives to effectively enhance teachers' pedagogical capabilities across diverse backgrounds. © 2025 Mathematics Education Research Group of Australasia, Inc.