This paper aims to explore how the use of lesson study approach with a constructivist framework could enhance Year 9 students' conceptions of pressure specifically on the topic of manometer reading in determining gas pressure. A diagnostic test was first administered to three Year 10 classes to help teachers identify student difficulties in learning the topic. Four cycles of lesson study was carried out on four classes, three from one school and an additional confirmatory cycle conducted in a class from a different school. Four tests of pre-, post, delayed and confirmatory were conducted in order to identify students' misconceptions and their conceptual understanding. The results of the study showed that with the use of the improved lesson design positive progress were achieved on the understanding of pressure to assist the reading of manometers to determine gas pressure.