This article shares information from a research study with six high school mathematics teachers focused onthe elements that helped and/orhindered their ability to implement formative assessment practices,including learning targets, questioning, feedback,self-assessment, peer assessment, and instructional decisions in their classrooms. Although this study was focused on mathematics teachers, thelessons learnedare relevant to teachers of othercontent areas and grade levels. Most of the supports andobstacles named by the teacherswereperceived as external to them. This impliesthatschool leaders can supportteachers as they incorporate these instructional practices.