This paper investigates how test-based, standardized accountability is impacting on urban school leaders' everyday work in Ontario and British Columbia, Canada. This critical policy analysis draws on theories of new public management and governmentality to document the experiences of school leaders as they enact and navigate test-based accountability policies. The data for this empirical study was collected from semi-structured interviews with 18 school leaders in 4 high schools from two cities: Toronto and Vancouver. As a result of different education policy contexts in Ontario and British Columbia, findings reveal that there were both similarities and differences between the experiences of school leaders therein. In Ontario, school leaders face tremendous pressure to provide evidence of improved test scores as part of an accountability regime that is high-stakes. In both provincial contexts, the mediatization of test scores places new demands on school leaders who act as entrepreneurs, marketing and selling their schools. Ultimately, the research highlights the unintended consequences of test-based accountability systems as contributing to the marketization of education in Canada with deleterious consequences for marginalized communities and the practice of social justice leadership in schools. There is a need to identify democratic and holistic measures of accountability.