The Classroom Assessment Scoring System (CLASS; Pianta et al., 2008) is a popular measure of teacher-child interactions. Despite its prominence, CLASS scores have fairly weak relations with various child outcomes (e.g., Zaslow et al., 2010). One potential reason for these findings could be systematic differences in observer severity. As such, the purpose of this study was to explore the scope and impact of rater effects on CLASS scores with a sample of 77 teachers who were rated by 13 observers. Results indicated significant rater effects across all three CLASS domains. Adjusting for these effects, however, did not improve relations between CLASS scores and child outcomes. Implications for the CLASS and related assessments are discussed.