In STEM (Science, Technology, Engineering, and Mathematics) professional careers, where projects are often complex and multidisciplinary, skills such as teamwork and leadership become essential for professional success. The current job market demands professionals who possess not only strong technical knowledge but also the so-called ‘soft skills’ that enable them to perform effectively in collaborative work environments, where teamwork and both managing oneself and others are key.

However, the development of these competencies remains a significant challenge within the curricula of technological universities. In this context, our paper presents a teaching experience with third-year engineering students at a technological university in Spain, aimed at developing the transversal competency of "leadership and teamwork." The activity was organized within the Design Thinking methodology and implemented through the Marshmallow Challenge, a collaborative exercise that encourages teamwork and fosters leadership skills.

Students were divided into teams of five and challenged to build the tallest structure possible in 18 minutes using only spaghetti, tape, string, and a marshmallow to place on top. Moments of success and collapse of the structure were photographed. Once the activity was over, the photos were projected, and a group reflection session was held in which participants were asked to share their experiences, identify the roles assumed by each team member, and analyze the factors that had an impact on the development of teamwork and the emergence of leadership in any member. Afterward, they were projected so that the teams could observe how the challenge had developed and draw their conclusions.

The results revealed something similar to previous experiences: teams that built and iterated prototypes quickly achieved better results than those that spent too much time on initial planning. Some teams took ideas from others around them. This happened more to avoid failure than to achieve success. That is, it was observed that the teams that took an example from what was happening around them did so when they saw the tower of a nearby team collapse. Each failed prototype of the team itself or those around it was an opportunity for further improvement. Students identified key elements of successful teamwork: emergent leadership, clear communication, and distribution of tasks. In contrast, in some cases, time pressure, limited materials, and authoritarian behavior when happened were identified as barriers.

The Marshmallow Challenge is a highly effective educational tool for simulating real-life, high-pressure teamwork scenarios where leadership skills can arise. It promotes meaningful learning and dynamically enhances those transversal skills in a playful manner. We recommend the integration of these kinds of activities at various stages of the engineering curriculum. Given that students in this field often encounter limited opportunities for such engagement, it is essential to create pathways for developing soft skills.

Keywords: Teamwork and leadership, transversal competency, Marshmallow challenge, active learning.