Large-scale, robust implementation of teacher data-driven decision making (DDDM) is a challenging endeavor, impeded by numerous organizational, and teacher, factors. One well-documented barrier to teacher DDDM is underdevelopment of teacher data literacy. This study examines common errors made by pre-service elementary teachers in the formulation of evidence-based claims about student cognition (e.g. student strengths and weaknesses relative to content mastery) in a United States of America context. Teachers in the sample commonly made several errors in the articulation of evidence-based claims based on classroom assessments, including providing nonspecific, irrelevant evidence for claims, and misinterpreting statistical evidence. Specific implications for pre-service teacher education and future research are discussed.