Trust among teachers is an important aspect of the capacity for reform in schools. In previous research, trust has traditionally been considered as a monolithic variable that characterizes this special element as a relationship across a school (Bryk & Schneider, 2002, 2003; Goddard, 2003; Kochanek, 2005). However, this study proposes that the trust necessary for instructional improvement is best understood as either a process of holding certain perceptions and anticipation of the reliability of the other party or as a product of accumulated opportunities for meeting professional obligations within professional learning communities (PLCs). Little research has explored the relationship between teacher-principal trust and the pattern of professional interactions among teachers and the principal. Using social network data on the professional relations between teachers and principals in four Midwestern K-6 schools, this study explores how social capital (Coleman, 1988, 1990) is distributed differently among teachers and the principal by school PLCs. A review of literature on trust and social capital reinforces the importance of school leaders that promote higher levels of trust among the teachers. Social capital as a concept and social network analysis as an instrument have been used in the field of education but seldom have they been applied to examine the relationships between principals and teachers. Findings of this study suggest that: (1) the effect of teachers' trust for the principal becomes less important when distributed leadership is present across major human resources that are visible and accessible for teachers; (2) the effect of principal leadership on influencing instructional capacity in PLCs can be seen through these kinds of social network analyses (Borgatti, Everett, & Freeman, 2002); and (3) the presence or absence of trust between teachers and principals around subject matter point toward areas where leaders and teachers bridge existing expertise to address new problems of instructional improvement. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]