Transdisciplinary (TD) graduate training programs are growing in number, yet little is known about their effectiveness or the development of TD attitudes and behaviors among students over time. This prospective longitudinal mixed methods study compares graduate students participating in a federally funded TD training program with non-participating students from the same disciplines and degree programs (n = 26). The Interdisciplinary Perspectives Index (IPI) and Behavior Change Collaborative Activity Index (BCCAI) were used to assess TD attitudes and behaviors at beginning, middle, and end of an MPH/PhD program. Additionally, a multiple case-based approach was used to further analyze changes among the TD students at three time points (n = 10), including a novel sketch protocol to elicit TD student conceptualizations (mental maps) of TD teams. Four assessments were used to construct an overall TD orientation score. Wilcoxon Signed Rank Tests showed TD behaviors increased over time only among TD students, and favorable TD attitudes were high at baseline and did not change for any group. Generalized Estimating Equations showed that TD behaviors were higher among TD students than traditional students at both mid and endpoint, with no difference at baseline. Visual assessments showed TD students' mental maps of TD research and team science, elicited under a novel sketch protocol, reflected greater integration and organization by endpoint. Two developmental patterns of increasing overall TD orientation emerged among the TD students. This article reports findings and insights applicable to TD graduate education and curriculum design and introduces a novel visual assessment tool.