This paper presents a mixed-method approach to measuring the functioning of Safe Schools/Healthy Students (SS/HS) Initiative partnerships. The SS/HS national evaluation team developed a survey to collect partners' perceptions of functioning within SS/HS partnerships. Average partnership functioning scores were used to rank each site from lowest to highest. Sites with the "most favorable perceptions of partnership functioning" were defined as having average scores in the top 10% (n = 10) and sites with the "least favorable perceptions of partnership functioning" were defined as having average scores in the bottom 10% (n = 10). Qualitative data for these 20 sites were inductively open coded for emergent themes and analyzed for patterns using grounded theory approach. Six themes emerged that distinguished sites reporting the most favorable and least favorable perceptions of partnership functioning: partner engagement, facilitators, barriers, shared decision making, partnership structure, and sustainability. Sites reporting the most favorable perceptions of partnership functioning effectively utilized collaboration processes that facilitate coalition building, such as shared decision making, effective communication, and developing a clearly defined structure. Qualitative themes from this analysis provide evidence of validity for the partnership functioning scale used and illustrate distinguishing features between sites with the most favorable and least favorable perceptions of partnership functioning. (Contains 1 figure.)