The paper examines the breadth and quality of formative assessment implementation of 202 mathematics and science teachers who participated in a two-year, school-based professional development programme that focused on formative assessment. Results are triangulated using three sources of data: baseline and end-of-Year 2 data from an annual survey, logs that were completed daily at six two-week time points and reflections on formative assessment techniques that the teachers wrote weekly during the log collection periods. The data indicate that while teachers made significant improvements in some areas, certain aspects of formative assessment are less emphasised and there are some patterns around quality of implementation that suggest more targeted professional development is warranted.