Construct maps are important tools in educational assessment and can serve multiple purposes related to development and validation as well as score interpretation and use. This chapter outlines a process for developing a construct map from the qualitative ordering of teachers’ responses to open-ended assessment items. The construct of interest pertains to a teacher’s ability to attend to what students say and do, which is a key component of many recommendations for instructional practice within mathematics education. The instrument we are developing is designed to measure teachers’ attentiveness to student thinking in quantitative reasoning problem situations. A key aspect of our instrument development process is the development of a construct map that hierarchically orders qualitatively different levels of teacher attentiveness. In this chapter, we describe our process for developing the construct map with the intent of providing an example to others who may be interested in engaging in the development of construct maps.