Teacher assessment decision making is described as a process that may be important in developing a measurement theory for classroom assessment. Teacher beliefs and values about what and how to assess often conflict with the pressures of external demands, especially recent high‐stakes large‐scale testing. With this sense of tension, teachers make assessment decisions that will engage and motivate students and enhance learning. Implications for a measurement theory of classroom assessment, as well as teacher preservice and inservice, are explored. The article suggests that measurement specialists need to adapt technical testing principles to be more relevant to the nature of classroom assessment decision making.