College courses are attempting to apply three-dimensional learning to both the instruction and assessment. This transformative way engages students in doing scientific practices and deepening disciplinary knowledge in physics. We used Evidence-Centered Design and the Three-Dimensional Learning Assessment Protocol to assess students’ ability to engage in the scientific practice of Planning Investigations. We conducted a written exam and Think-Aloud interviews to collect data from physics students in introductory college course. We analyzed interviews using the lenses of planning theory and model-based reasoning in laboratory. The analysis helped us to identify the model of planning investigations process conducted by college students during assessment. Results from this analysis will help us interpret students’ written work and support the development of assessment tasks in the future.