We examined all available observer reports on the problem solving lessons and elicited all references to sample student work. These comments were then categorized under specific themes such as ‘Errors in Sample Student Work’ or ‘Questions for students to answer about sample student work’. Additionally, observers completed a questionnaire (Figure 5) designed specifically to help designers better understand how teachers use the sample student work and the supporting guide, and how this use has evolved over the course of the project. This data forms the basis of the findings from the US lesson trials.