Open inquiry learning is a pupil-centred approach in which pupils generate investigable questions for the purpose of planning and implementing their own science investigation. However, generating investigable questions is not an easy task and requires a structured approach. Therefore, this study was conducted to improve the practice of a teacher-researcher in developing an Investigable Question Formulation Technique (IQFT) in a Malaysian school. This article attempts to answer the following research question: How can a teacher-researcher develop an Investigable Question Formulation Technique (IQFT) to facilitate pupils in generating investigable questions? IQFT, the intervention introduced in this study, contains eight main steps, which were carried out in two cycles. These steps involved the processes of (i) planning action, (ii) taking action, (iii) collecting and analysing data and (iv) reflecting. Unstructured observations, pictures and pupils’ writing were among the data collected. Narrative analysis was conducted, to describe how the teacher-researcher applied IQFT as an approach to facilitate pupils developing investigable questions. Despite pupils being able to formulate investigable questions using IQFT, the teacher-researcher realised that pupils need to be continuously trained in this area. In addition, the teacher-researcher found that teachers need to adapt the educational approach according to the teaching context, to enhance the learning outcomes.