This paper discusses upper primary school teachers' perspectives on changes to their knowledge and practice through participation in a design-based research project. It analyses their experiences using Clarke and Hollingsworth's (2002) empirically-founded model for professional growth to understand more about the mechanisms for change that might support teachers in teaching a challenging aspect of mathematics--algebra. The ten teachers referred to observations of teaching in action, and modification of their beliefs about algebra, themselves as learners, about particular students, and about teaching mathematics. They shared differing perspectives on interacting with colleagues. Some teachers described discomfort when confronted with their lack of knowledge or with their students' questions during lessons. The findings demonstrate pathways that appeared to be commonly experienced by many of the teachers and also those that highlight the individualistic nature of teacher change mechanisms. Implications for the design of professional learning in mathematics for in-service and pre-service teachers are discussed.