This study developed the Investigable Questioning Formulation Technique (IQFT) protocol to formulate investigable questions by following the procedures of design-based research. As guiding heuristics, the protocol used two provisional design principles based on teaching experience and previous studies that have applied tools for formulating questions, notably, the question formulation technique, SMART goals, and a typology of investigable and non-investigable questions. Two cycles comprising six lesson interventions were completed with two groups (n = 23, n = 25) of students in the same school in Malaysia. Questions were analyzed using qualitative content analysis and a question typology framework. Findings show the majority of students formulated comparison, exploratory, and validation of mental model questions. Some questions were posed in the prediction, descriptive, and problem-solving categories, but none were categorized as cause and effect, design and make, or pattern seeking. Implications for use of the IQFT protocol to help facilitate Malaysian students' generation of investigable questions, design experiments, and implement open inquiry are discussed.