This paper reports on the findings of a pilot school-based professional development programme for Tanzanian primary school teachers launched in February 2011 and evaluated in December 2012 by the Ministry of Education and Vocational Training with the support of UNICEF. The study set out to investigate the effectiveness and efficiency of the pilot programme in changing pedagogical practices before it was scaled up nationally. It was found that teachers who had participated in the school-based training showed significant differences in their pedagogical practices and demonstrated a positive attitude towards their training and their pupils, and saw teaching and learning as an interactive, communicative process. Drawing on the findings, the paper explores the challenges and the lessons learned for scaling up school-based teacher development at the national level in Tanzania and other countries in the east and southern African region.