A goal of this double issue of English Teaching: Practice and Critique is to collectively consider what we mean when we talk about knowledge about language. How have our understandings changed over time? What are the implications of these new understandings for pedagogy in the field of language teaching? These are necessary and important questions. This article, however, does not attempt to address them. Rather, it focuses on the power of standardized assessment in language education and on its implications for the discussions contained within this journal. Central to this paper is the argument that standardized language assessments are resistant to change, rarely integrating new understandings of language into assessment designs. This reticence in turn limits advances in pedagogy. Language theorists and educators are therefore compelled to advocate for assessment reform. Drawing on a study of government-mandated writing assessment and its impact on Grade 12 academic students in Alberta, Canada, this article demonstrates how poorly developed standardized assessments curtail teaching and learning. The article concludes with a discussion of validity theory and its implications for test design, demonstrating how validity research can be used to ensure that standardized language tests value and support new understandings of language theory.