Textbooks can be viewed as mediators between the intentions of policymakers and classroom teachers. We report here on a study in which textbook tasks and the opportunities for learning they afford were used as a lens through which the impact of the Project Maths curriculum reform in Ireland was observed. A total of 7635 tasks on the topics of Differential Calculus and Patterns, Sequences and Series in the three most widely used post-primary textbook series (pre- and post-reform) were examined using Lithner’s reasoning framework. An analysis of the reasoning required to successfully solve these tasks concluded that 92% of the tasks required imitative reasoning alone, while only 8% of tasks required creative reasoning. There was, however, a statistically significant increase in the percentage of tasks requiring creative reasoning between the pre-Project Maths textbooks (4.5%) and those published post-Project Maths (11%). Nevertheless, our results indicate that learners are not being provided with sufficient opportunities to develop reasoning skills central to the reform agenda and that the textbooks examined did not successfully mediate the reform envisaged.