This study examines science teachers' thinking on the nature and purpose of practical work in the context of the National Curriculum for Science in England. There is a particular focus on investigations (enquiry in the science classroom), which have been a statutory component of the curriculum since 1989. Data were collected through individual interviews with science teachers about their classroom practice. The findings suggest that little attention is being given to procedural understanding in terms of ideas relating to the quality of data. It is argued that this is a key limiting factor in the development of pupils' ability to engage in genuine investigative work.