For many of us, not having data concerning a client’s progress during treatment is tantamount to being unprepared for a lecture, or showing up at a birthday party without a present—totally unthinkable. This zealous position is based on the assumption that clinical decisions regarding treatment efficacy should be based on data. Data, in this case, refers to both quantitative and qualitative information that provides evidence for deciding the course of treatment. This is not to say that data can and should be collected on every aspect of the clinical process. Indeed, intuitive decision-making on the part of the speech-language pathologist is often warranted. But in general, a series of decisions regarding whether or not treatment is working, can and should be based on data. This article examines the ways in which we can measure treatment progress, and provides guidelines for the reader in the use of a data-based, decision-making model.