What is the purpose of this experiment? Or can students learn something from doing experiments?

Historically there have been many claims made about the value of laboratory work in schools, yet research shows that it often achieves little meaningful learning by students. One reason, among many, for this failing is that students often do not know the ''purposes'' for these tasks. By purposes we mean the intentions the teacher has for the activity when she/he decides to use it with a particular class at a particular time. This we contrast with the ''aims'' of a laboratory activity, the often quite formalised statements about the intended endpoint of the activity that are too often the ''opening lines'' of a student laboratory report and are simply the ''expected'' specific science content knowledge outcomes—not necessarily learnt nor understood. This paper describes a unit of laboratory work which was unusual in that the teacher's purpose was to develop students' understanding about the way scientific facts are established with little expectation that they would understand the science content involved in the experiments. The unit was very successful from both a cognitive and affective perspective. An important feature was the way in which students gradually came to understand the teacher's purpose as they proceeded through the unit. fl 2000 John Wiley & Sons, Inc. J Res Sci Teach 37: 655 - 675, 2000 The research we report here focuses on the work of a highly informed and experienced science teacher (the first author) who sought to address her concerns about laboratory work. As we explain below, the study was a collaborative one in which the teacher and the researchers worked closely together as a research team, and the voices of both teacher and researchers are presented.