Teamwork skills are important contributors to classroom learning outcomes and graduate employability. Although much has been reported in the literature about the components and characteristics of effective marketing student teams, less is known about how such knowledge is conceptualized and cultivated by frontline marketing instructors. This study applies a perspective of tacit theory to in-depth interviews with frontline instructors in undergraduate marketing courses. Our findings, summarized in a framework of adaptive cultivation of effective teams (ACET), highlight how instructors perceive effective teamwork as a dynamic interaction between three interwoven components of team effectiveness (team composition, team member behavior, and team culture) and adjust their interventions across these components. Overall, this study uncovers instructors' tacit theories of cultivating effective marketing student teams, and how these tacit theories impact in-class practices.