Vygotksy's theory on concept formation was used for teaching forces to 102 eleven-year-olds in the UK. Students' progress was assessed using a pre- and post-instruction questionnaire and was compared to the progress made by 129 students in comparison classes. On most measures, progress in the intervention classes was significantly greater than in comparison classes. Observation notes and tape-recording data were analysed to help explain the differences found in the students' progress. The analysis of these data indicates that students in the intervention classes spent considerably more time using the scientific ideas. In addition, in the intervention classes students' alternative ideas were addressed and the teacher ‘scaffolded' students' use of the scientific ideas. The results of this study indicate the potential that the principles used to design this teaching-learning sequence may be applicable in other content areas of science instruction.