This paper reports on a research project undertaken with a group (n=19) of Irish pre-service student teachers (PSTs) during the third year of a four-year undergraduate education course. A series of workshops were carried out on the critical evaluation and design of mathematics tasks. The research is presented as a case study using mixed methods to gather data. Through critically evaluating and designing mathematics tasks PSTs developed knowledge of cognitive demand, pedagogical design capacity and showed evidence of developing curriculum-making competences. The research highlights the need for PSTs to work together on evaluating and designing tasks.