Teachers' social capital is defined as "the knowledge and resources for teaching practice accessible through a social network." The first step to analyzing teachers' social capital is to understand the structure of their social network. Some networks are highly interconnected, offering teachers numerous opportunities to share ideas and receive feedback. Other social networks are more loosely connected. In these networks, teachers can become isolated from their colleagues, and it can be harder for them to work collaboratively to improve teacher and student learning. The strength of a teacher's professional learning community cannot, however, be measured by just the number and arrangement of connections. Instead, researchers must be able to describe what these connections offer teachers in terms of resources that can be used to support teacher and student learning. Teacher learning involves accessing and acting on these resources. Professional development can support this process by increasing the amount of social capital available to the teachers in a school community. Teacher conversations, according to social capital theory, must be characterized by expertise, reciprocity, and relevance in order to best support teacher learning.