This paper examines the impact of a series of design changes to an online mathematics education course in terms of transactional distance between learner and teachers, pre-service education students' attitudes towards mathematics, and their development of mathematical pedagogical knowledge. Transactional distance theory (TDT) was utilised to investigate and describe the interactions among course structure, course dialogue and student autonomy in an online course over a two-year period. Findings indicate that Web 2.0 technologies, when used thoughtfully by teachers, can afford high levels of structure and dialogue. Feedback from pre-service teachers indicated an improved attitude towards mathematics and an increase in their mathematical pedagogical content knowledge. These findings have implications for universities moving towards the delivery of teacher education courses entirely online.