This study was designed to find out why students may fail to learn from teacher demonstrations. In the context of an interpretive study in an Australian senior-year physics course, data were collected to understand the constraints that mediated learning about rotational motion. Over a period of 6 weeks, we gathered observational data, videotapes of classroom transactions, interviews with students and the teacher, and students' notebooks. Our analysis revealed six dimensions that may have prevented students from learning what the teacher had intended. These dimensions included (a) students' lack of theoretical framework to separate signals--the phenomena--from noise, (b) interference of discourses learned in other contexts of the physics course, (c) interference from other demonstrations and images that had some surface resemblance, (d) students' problems in piecing together coherent representational frameworks from the information given, (e) low salience of knowledge related to demonstrations on tests, and (f) lack of opportunities for students to test their descriptions and explanations. A set of recommendations is presented designed to facilitate teachers in changing their perspective on demonstrations and their associated practices for improving student learning. The recommendations are embedded in a framework that allows teacher reflection and action research.