The professional development for teachers is an important component of the quality of education. However, few systems for monitoring and analysing the quality and impact of teacher professional development programmes have been created. In this article, we present the effects on classroom practices of a Colombian professional development programme for in-service secondary mathematics teachers. We compare the teachers' classroom practices of planning, implementation, and assessment, before and after participating in the programme. We found that the professional development programme shows a statistically significant and positive effect on planning, implementing and assessment practices. These results serve as evidence of teacher training policy in terms of changes in classroom practices.