The findings discussed here are a small part of a larger study entitled, "Encouraging Persistence Maintaining Challenge". The paper reports five teachers' observations of the implementation of a task which was new to them. The teachers were asked to identify aspects of the task which they perceived as challenging for the Year 6 students. The teachers' responses are discussed using a framework of features of challenging tasks proposed by Sullivan et al. (2011). The findings show that teachers identified the challenges involved as demanding mathematical reasoning, interpreting complex mathematics and in expecting students to create their own solution pathways.