This study examined changes in beliefs and confidence of 24 pre-service mathematics teachers after they participated in professional learning in an algebra pedagogy course, which addressed an under-researched area about their domain-specific beliefs in teaching algebra. A single-group pretest-posttest design was adopted. Quantitative data were collected to measure beliefs and confidence in teaching algebra, and qualitative data were used to help interpret and understand the results obtained from the quantitative research. Quantitative data analysis demonstrated significantly less change in beliefs than in confidence. Qualitative data analysis identified two themes accounting for changes in beliefs (learning various pedagogies and conceptually oriented teaching) and four themes accounting for changes in confidence (understanding students' learning needs, acquisition of pedagogical knowledge and approaches, designing engaging mathematical activities and tasks, and discussion with teacher and students). The course helped shift teachers' beliefs from an emphasis on performance to one on understanding and an increase in pedagogical content knowledge in algebra resulted in increased teachers' confidence. This study highlights the key to changing beliefs and confidence and the necessity of progressing from a dualistic to a relativistic orientation towards mathematics teaching.