Increasingly, educational systems are appreciating the importance of middle leaders leading educational improvement in schools. Schools depend on middle leaders to lead site-based educational development in areas including curriculum development, teacher professional learning and student learning improvement. Middle leaders are in a unique but complex position where they influence both executive leadership and teachers within the school organisation. Adopting case study methodology to investigate the practices and influence of middle leaders leading a school-based educational development project, three semi-structured interviews and artefacts from two middle leaders were collected over eight months. The theory of practice architectures afforded an examination of data to explain the conditions and arrangements enabling and constraining the middle leaders' practices of influence. The findings showed middle leaders' influence was dependent on executive leadership support, time, formal role descriptions and trusting relationship. Furthermore, the results reveal middle leaders can influence educational development at the school level through advocating for, collaborating with, and empowering colleagues to support teacher ownership of site-based projects. Of interest, this study showed influence can be reciprocal, between middle leaders and colleagues, and between middle leaders and executive leadership.