Purpose: The study investigates the ways in which principals engage with, and attend to, the data-driven accountability measures of No Child Left Behind (NCLB) and local mandates. Theoretical framework: The study is framed with the notion of assemblage, a term often associated with actor-network theory (ANT)—a theory that focuses analytic attention on how disparate actors, material, and discursive practices come together to form dynamic associations. Within the assemblage, principals are situated as bricoleurs. Research methods and data: Data for analysis come from interviews conducted with 45 New York City principals between June 2005 and October 2008 as part of a larger ethnographic study examining NCLB, and a series of interviews with 12 of the 45 principals, conducted annually through March 2012. District surveys, various documents, and field notes of participant observation also inform the study. Findings: Principals play active policy roles in negotiating federal regulations and local initiatives, as well as selectively performing assessment and accountability mandates. Principals, who have often been cast in the media as either dupes of the state or as active resistors, negotiate and appropriate external accountability in innovative, sometimes savvy, ways. Implications for practice and research: Principals need to consider institutional circumstances and external accountability not as boundaries or constraints, but rather as available material with which to respond. Future research should aim to examine the ways in which principals engage with data and accountability demands via reflexive interactions with different types of knowledge, mediating artifacts, and methods.