As students gain more experience with design concepts, they should progress from novice to expert design thinkers. The purpose of this research was to identify the constructs of growth in design thinking (DT) over short- (one weekend) and long-term (10 weeks) design challenges. A DT mindset questionnaire was completed by students in a third-year undergraduate biomedical design course at the beginning of the course, after a one-weekend design challenge, and on completion of the course. After the short design challenge, an improvement in 15 of the 19 constructs was observed relative to baseline. Six of these constructs: mindfulness and awareness of the process, embracing risk, abductive thinking, envisioning new things, creative confidence, and optimism to make an impact, were sustained over the course of the semester indicating that a prolonged period of experiential learning can maintain short-term gains in DT. Three of the constructs: holistic views (considering the problem as a whole), diversity, and curiosity showed improvement following the short-term design challenge, then deterioration suggesting that situational circumstances are significant contributors to these constructs of DT. DT generally improves with the opportunity to collaborate, communicate, and design for a specific outcome. However, situational factors including team diversity, instructor expertise, dedicated time for team collaboration, and prior experiences can affect changes in the DT skillset.