This study reports teachers' insights and challenges after one year of adopting a curricular material designed to move students through carefully engineered, small steps and encourage learners through success and accessible challenges. The analysis of interviews showed that teachers 'followed' the material in different ways, not necessary in-line with its underlying principles. Two of these principles--bonusing and breaking down concepts into smaller elements--were particularly difficult for many teachers, suggesting the need of a specific teachers' mathematical knowledge. [The authors acknowledge the support provided by Canadian Oil Sands Limited. For the complete proceedings, see ED583989.]