Teacher and headteacher assessments and professional development are deemed critical levers for improving quality education in an increasing number of countries and contexts. However, prioritising improvement is not always evident, given that sometimes those subjected to assessments are not effectively informed about their performance (e.g. from national teacher examinations) or how to improve their work via feedback. This paper explores the bridging role of feedback concerning teacher and headteacher assessments and continuing professional development in the Mexican context, where scarce research exists. This mixed-methods research contributes evaluation evidence of Mexico's 2013-2018 education reform, including high-stakes staff assessments and individual feedback reports. Survey data from 122 primary school teachers and headteachers and thirteen interviews with teachers, headteachers and policymakers indicate the feedback report made it difficult to distinguish between poor and proficient performance and identify strengths and weaknesses. Challenges regarding suitable continuing professional development following assessment feedback are put forward.