Demonstrations are a core part of science teaching. In 1980 a three-part assessment method using demonstrating was proposed. Known as DOE this consisted of demonstration, observation and explanation. DOE quickly evolved into POE: predict, observe, explain. In the light of experiences with POE and insights from constructivist theory we set out in this paper a learning-focused refinement of POE, namely PEOR: predict, explain, observe, react. We offer a theoretical justification for the value of PEOR and argue that it is more than a simple update of the earlier protocol. PEOR can be used with any age of students. We illustrate its use in practice with initial teacher education students working on the topic of forces and fields. The demonstration we describe is called "floating magnets". PEOR enabled the teacher to clarify students' current conceptions about the topic. We found that these surfaced naturally and served as an important start in the process of clarifying ideas about the broader course content. When using PEORs with student teachers, we also noted that students' affective and cognitive engagement in the activity was considerably greater than that shown during a traditional demonstration. (Contains 10 figures.)