Children who have difficulty learning to read are at increased risk for academic failure, poor self-esteem, anxiety and depression, and unemployment. To help reduce these risks, it is important to identify and treat weaknesses in a child's reading as early as possible. The aim of this study was to develop a valid and reliable comprehensive standardized test of a key reading sub-skill called grapheme-phoneme correspondence (GPC) knowledge. In Phase 1 of the study, we selected a comprehensive evidence-based list of the most important GPC rules for learning to read in English. In Phase 2, we administered this list to a representative sample of Australian children to calculate age- and grade-based norms. In Phase 3, we established that the test had robust inter-rater and test-retest reliability, and appropriate criterion validity. We hope that this new test, which is called the Letter-Sound Test, proves useful to clinicians, teachers, and researcher as a comprehensive test of GPC knowledge.