Current educational reforms call for higher student learning standards. The result is greater accountability for teaching and learning than ever before. School leadership mediates reform implementation so that the intent of the policy is transferred into teaching practice. I suggest that how teachers make sense of leadership reform activities affects their ability to modify teaching and learning in their classroom. Yet, management and accountability tasks consume the school administrators' time. A distribution of leadership is necessary to ensure that instructional reforms affect teaching practices in the classroom. The distribution of leadership varies from school to school. Thus, little is known about how leadership is distributed. Even less is known about how school leadership affects teachers and their teaching practice. Through this investigation I examine school leadership's effect on dimension of teaching capacity during instructional reform. I use a mixed-method case study of one urban Middle school to understand how teachers experience, both, distributed leadership and activities related to their practice during instructional reforms. I examined: 1) what school leadership for instructional improvement looks like, 2) sources of leadership teachers look to for support, and 3) the connectivity between distributed leadership and three dimensions of teaching capacity. This study highlights three major findings. First, leadership is distributed formally and informally, among people and tasks. Second, teachers seek administrators and other positional leaders for communicating expectations and providing resources. They look to informal teacher leaders within their peer groups for encouragement, practical support, and resources in areas that are more closely relate to classroom instruction. A third major finding is that dimensions of teaching capacity could be identified in three dimensions (human capital, social capital and decision capital). The enactment of distributed leadership has indirect, yet significant, effects on teachers. Dimension of teaching capacity can be manipulated by leadership to provide instructional support and increase teaching capacity during reform implementation. This suggests that school leadership could identify and refine reform activities to affect teaching and learning in the classroom. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]