Although social ties are a necessary condition for social capital, there is a dearth of research on the factors associated with the existence of such ties among school staff. Using a mixed-methods approach, we examined the role of both formal organizational infrastructure and individual characteristics in shaping advice and information interactions about instruction among school staff within and between schools. Our findings from social-network models showed that, while individual characteristics were associated with within- and between-school ties, aspects of the formal school organization had larger effects. Moreover, having a subject-specific leadership position most strongly predicted between-school ties. Our analysis of interview data supported and extended these findings, showing that leadership positions worked in tandem with other aspects of the organizational infrastructure, such as organizational routines, to influence school staff members' interactions about instruction.