Background/Context: Contemporary state and national policy rhetoric reflects increased press for "evidence-based" decision making within programs of teacher education, including admonitions that programs develop a "culture of evidence" in making decisions regarding policy and practice. Recent case study reports suggest that evidence-based decision making in teacher education involves far more than access to data--including a complex interplay of motivational, technical, and organizational factors. Purpose: In this paper we use a framework derived from Cultural Historical Activity Theory to describe changes in organizational practice within two teacher education programs as they began to use new sources of outcome data to make decisions about program design, curriculum and instruction. Research Design: We use a retrospective case study approach, drawing on interviews, observations and documents collected in two university programs undergoing evidence-based renewal. Conclusions: We argue for the value of a CHAT perspective as a tool for clarifying linkages between the highly abstract and rhetorically charged concept of a "culture of evidence" and concrete organizational practices in teacher education. We conclude that the meaning of a "culture of evidence" depends in large measure on the motivations underlying its development.