Background: Although there is consensus on the favourable impact of formative assessment (FA) on learning, it is unclear to what extent general FA strategies are directly applicable to the specific field of mathematics education. Objective: Study the relevance of a questionnaire which describes 26 FA practices supported by Wiliam’s model in the particular context of mathematics education. Design: Mixed, the frequency and feasibility are consulted through a questionnaire and in-depth interviews. Participants : Thirty in-service mathematics teachers answered the survey and of ten invited, three agreed to be interviewed. Data analysis : We carried out a descriptive analysis for quantitative data and qualitative thematic analysis. Results : The strategies of collecting evidence, feedback, collaboration, and self-regulated involvement in learning are viable and frequent in mathematics education, however, the strategy of clarifying and sharing goals requires adaptation to the context. In addition, nine novel FA practices are described. The implementation of formative assessment creates tensions with the summative function, it is laborious to implement and consequently takes time outside the classroom. Conclusion : We identified that FA practices are frequent and feasible to implement. Clarifying and sharing goals requires the adequacy of the mathematical context.