In recent years, John Hattie’s book Visible Learning (2009) has greatly influenced educational practitioners and policymakers. The visible learning approach has been deemed “the Holy Grail of teaching” (Mansell, 2008), and Hattie has been called the “messiah” of educational research (Evans, 2012). In this article, we outline some of the significant methodological problems embedded in Hattie’s work and relate them to his theoretical stance. We argue that his focus on single causal factors causes him to disregard important dimensions in educational practice. Furthermore, by analyzing parts of the primary research and the meta-analysis upon which Hattie grounds his conclusions, we find both serious methodological challenges and validity problems. We relate these problems to the technological rationality that informs Hattie’s work and implicitly constitutes his theoretical approach. Finally, we outline, among other things, how questions of human agency and intentionality for attending school become marginalized as the broader consequences of using Hattie’s approach to institutionally organize teaching processes. Another consequence of Hattie’s work is that educational research begins with questions of methods rather than research into schools’ everyday teaching practices.