This thesis addresses the role of school organisational structures for teacher social capital and student outcome. The thesis is driven by a general concern over the widescale reforms Swedish schools have undergone in the last decades and particular concern over the so-called work unit reform. This reform was introduced to increase teachers' overall interactions by reorganising schools into mixed-subject teams where teachers of different subjects work together in student-centred work units. This study suggests that the reform has significantly reshaped teachers' opportunities to build social capital, impacting teachers' everyday professional learning and student outcomes. There are also indications that the reform poses a challenge to improving educational equity by reducing the educational achievement gap between students of high and low socioeconomic status (SES). The thesis comprises four individual studies addressing different aspects of this matter: two systematic literature reviews, one empirical construct development study, and one empirical study, each presented in separate academic journal articles. The first systematic review explored the uncharted intersection of literature on educational leadership, professional learning, and educational equity. Motivated by a concern for marginalised students' educational experiences and achievements, it investigated leadership approaches to shaping teachers' professional development and ongoing learning that support more equitable outcomes for students. Employing the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement and quality appraisal using the Weight of Evidence framework, 41 empirical articles were selected for detailed analysis. The outcome was five themes: Critical framing of social justice issues; Dialogue and enquiry; Learning and identity development; Context, resources, and motivations; Normalising inclusion and shared leadership. These five themes were identified as helpful for educational leadership to address inequalities and promote educational equity. The themes were seen both as activities that are intentionally undertaken towards social justice and educational equity, and as the results of that intentionality. One theme was particularly informative for the overall aim of this thesis-the context, resources, and motivations of teachers and leadership for professional learning. These contexts, especially the institutional, political, and school contexts, were also imminent historical factors motivating the present thesis. The second systematic review synthesises research on teacher social capital and professional learning. Employing the same combination of the PRISMA Statement and the Weight of Evidence framework for quality and relevance appraisal, the study made an in-depth analysis of 66 empirical articles. The review finds that social capital among teachers has been associated with 1) teacher professional development, 2) the implementation of change, 3) the introduction of new and beginning teachers, 4) teacher retention and job satisfaction, and 5) improved student achievement. These have, in turn, been associated with the implicit outcome of promoting educational equity. Moreover, the review points to the critical role of school organisational structures in promoting different social capital dimensions, such as bonding, bridging, and linking. The review calls for research exploring the relationship between these dimensions and schools' organisational structures to promote the beneficial outcomes of teacher social capital, such as improved student outcome and educational equity. Article 3 is an empirical construct development study that addresses the lack of measures that enable empirical testing of relationships between organisational structures and the subdimensions of social capital. Using survey data from 228 Swedish teachers, the study develops and tests latent constructs that capture teachers' internal (bonding), external (bridging), and vertical social capital (linking). It also provides measures for teachers' formal and informal organisational structures. Empirical results show that organisational structures predict teachers' overall social capital, and that formal and informal structures promote teachers' internal, external, and vertical social capital to a varying degree. Furthermore, by contrasting teachers in work units and subject departments, striking differences were revealed, and the context-sensitivity of the measures was confirmed. Article 4 is an empirical study that employs the measures developed and validated in Article 3 to analyse the role of school organisational structures and teacher social capital for student outcome. The study used student outcome data and survey data from 359 teachers in 40 teacher teams in Sweden. The nested nature of the data enabled analysis of both within- and between-group effects of the different social capital dimensions and the formal and informal organisational structures. A multiple regression model tested the direct effects of internal, external, and vertical social capital on student outcome at the teacher and team levels. Findings show that only the internal dimension of social capital positively affects student outcome, and that the effect is more substantial at the team level. Furthermore, a multilevel mediation model showed a positive indirect effect of formal organisational structures on student outcome via internal social capital. However, informal organisational structures have a direct negative effect on student outcome. Contrasting teachers in different team types, striking differences were found. Teachers in work units have less opportunity to bond with subject peers within their immediate groups of belonging, which is vital for building internal social capital. Meanwhile, the results of this study show that it is the internal social capital among teachers that will positively affect student outcome. At the same time, teachers in work units build more external social capital by bridging with subject peers in other work units. However, these interactions do not affect student outcome. In other words, teacher social capital is unbound. In addition, teachers in work units have generally lower levels of human capital in terms of experience and tenure than subject department teachers. Yet they are more dependent on their human capital for improving student outcome. This poses a challenge to schools in disadvantaged settings, where turnover rates are higher, and teachers' human capital is generally lower. While work unit teachers are more dependent on their human capital for promoting student outcome, the effect of formal organisational structures on student outcome is both positive and direct for subject department teachers. The findings from the empirical studies have important practical implications. They send an important message to policymakers and school leaders: in order to improve student outcome, teachers should be provided with opportunities to build internal social capital, and that the schools' formal organisational structures play a vital role in shaping the conditions for such opportunities. This thesis also makes significant theoretical and methodological contributions. First, it provides a theoretical account of leadership approaches promoting professional learning and educational equity. Second, it provides a deepened understanding of the importance of social capital among teachers for several beneficial outcomes, such as improved professional learning and student outcomes. Third, it provides a refined conceptualisation of teacher social capital that includes the dimensions of bonding, bridging, and linking for building internal, external, and vertical social capital. Fourth, it makes a methodological contribution by developing and validating measures of teachers' internal, external, and vertical social capital as well as their ' formal and informal organisational structures. These measures are context-sensitive and can be used in other national settings and school systems.