This article introduces and applies a methodology to analyze the effect of team diversity on team design cognition. We explore team diversity in relation to team members’ gender. We studied two types of teams: heterogeneous teams composed of one female and one male mechanical engineering students and homogeneous teams of two male mechanical engineering students. We analyzed 28 design protocols using the Function-Behavior-Structure ontology to code protocols and measure team cognitive design behavior. We found that male design students in the mixed teams tend to dominate the design activity. Also, we found that mixed teams showed significantly more co-design activity compared to male only teams.