Prior to the mandatory testing and reporting required by the No Child Left Behind Act (NCLB), school improvement efforts were shown to lack coherence (Newman, Smith, Allensworth, & Bryk, 2001) and often included conflicting programs (Hatch, 2002). Part of the theory of performance-based accountability in general, and NCLB in particular, was based on the belief that regular and comprehensive evidence would help to focus these efforts. Research seems to indicate, however, that individuals vary widely in their assumptions about the value and purpose of evidence (Coburn & Talbert, 2006), that it is often difficult to identify students' challenges based on the resulting annual data (Black & Wiliam, 1998), and that searches for meaningful remedies to real or imagined problems are often extremely limited, somewhat chaotic, and frequently lead back to familiar practices as opposed to real change or innovation (Gross, Kirst, Holland, & Luschei, 2005). In this CPRE Policy Brief, the authors examine the extent to which the assumptions in the law manifest themselves in the actions that school leaders take. This brief asks and answers the question: How do school leaders--administrators and teachers--respond to the results of state assessment systems and the pressure of performance-based accountability? And do those responses seem to matter to achievement outcomes? Data Collection Information is appended.