Systematic quantitative research on measuring distributed leadership is scarce. In this study, the Distributed Leadership Inventory (DLI) was developed and evaluated to investigate leadership team characteristics and distribution of leadership functions between formally designed leadership positions in large secondary schools. The DLI was presented to a sample of 2,198 respondents in 46 secondary schools. The input from a first subsample was used to perform exploratory factor analyses; the second subsample was used to verify the factor structure via confirmatory factor analysis. A one-factor structure for the leadership team characteristics (coherent leadership team) and a two-factor structure for the leadership functions (support and supervision) were confirmed. The results of the DLI underpin that leading schools involve multiple individuals, which differs by the type of function. (Contains 5 tables.)