The purpose of this study was to determine whether preservice teachers can be trained to be more clear during instruction and whether a causal relationship exists between teacher clarity and student achievement. A review of literature in teacher education, business, and industrial training revealed that no intact, empirically verified training regimen exists. As a result, training research findings were aggregated to construct a model, the Clarity Training Program (CTP), which would provide skill development in the appropriate use of 17 specific teacher behaviors that make instruction clearer. Preservice teachers (N=73), enrolled in four sections of an educational methods course, were randomly assigned to treatment in a modified Solomon Four Group design. Experimental group teachers received 8 weeks of training in the use of the 17 behaviors which make instruction clearer. Before and after training, subjects taught short lessons while being videotaped; learners completed tests of content and rated their satisfaction with the teaching. Statistical analyses revealed that training brought about highly significant improvements in teachers' clarity and ability to produce student learning. Data, including a list of discriminating clarifying behaviors, are displayed in six tables. (SM)