This paper describes the design and results of a study carried out with elementary pupils ages 8-9 years on the topic of sinking and floating, with the aim of checking the validity of a general scheme for classroom activities based on a constructivist perspective. Children's "ways of looking" at buoyancy and the production of materials that could be used for elementary school teacher training were investigated. The idea of conceptual change as the basis of the scheme and the importance of conceptual change in teacher training are discussed. The three phases of the scheme, "messing about,""intervention," and "reflection," are discussed. The introduction is followed by a presentation of the aims, methods, and data sources of the study. A summary of the results obtained and a discussion of some general issues concerning the role of educational research towards school practice conclude the paper. Two flowcharts and a 27-item bibliography are attached. (KR)