Freehand sketching meets a vital need in design for fluid, fast and flexible visual representations that designers build off of and learn from. Sketching more frequently during the design process correlates with positive design outcomes. Engineering designers receive minimal training on freehand sketching, and engineering students do not apply freehand sketching well during the design process. This study examines some of the underlying factors associated with using sketching more frequently. We examine how sketching skills, spatial visualization skills, sketching instruction and engineering design self-efficacy influence designers’ self-reported sketching behavior. We find that higher sketching skills are associated with using sketching in a variety of ways, and spatial visualization skills and design self-efficacy are associated with sketching more frequently. The relationships uncovered were emphasized by their longevity: spatial skills and sketching skills in students’ first semesters predicted sketching more frequently in a senior capstone design course. These long-lasting relationships suggest the need to invest in students’ spatial skills and sketching skills early in the degree program so that they can be leveraged for better design practice.