This article draws on Kane's (2006) argument-based validation framework to synthesize evidence derived from a large-scale, mixed-method explanatory study on the impact of the Ontario Secondary School Literacy Test (OSSLT) on second language (L2) students. The purpose of the OSSLT is to ensure that students have acquired the essential reading and writing skills that apply to all subject areas in the Ontario provincial curriculum up to the end of Grade 9 in Canada. Kane's framework is used both to specify the proposed interpretations and uses of the OSSLT results by laying out the network of inferences and assumptions involved in this test and to elaborate whether the proposed interpretations and uses have been supported by empirical evidence from the study. Findings from the study show that the results of the OSSLT, a test constructed and normed for first language English speakers, should be interpreted differently and with caution for second language students. By synthesizing the empirical evidence within an argument-based validation framework, we can fully understand the impact of the OSSLT in relation to test design, test accommodation, and literacy classroom practices in the Canadian context.