School leaders increasingly view inquiry-based professional learning as a means to address diverse aspirations concerning teacher development, school improvement, and regulatory requirements. This qualitative, case study uses interview data to investigate the experiences of school leaders during a one-year cycle of "Practitioner Inquiry: Teacher as Researcher." Initially envisaged by the leaders as a solution to school improvement and compliance targets, the data reports how the practitioner inquiry professional learning initiative shifted to reinforce the leaders' role as expert classroom practitioners, and to be an innovative way to shape collegial reflexive practice. Viewed through the Trialectic Theory of Spatiality lens, this paper reports how leaders in one school setting negotiated the potentially contending educational spaces relating to routinised practice, school improvement, and compliance to shape "thirdspace" innovation.