The Teaching Strategies GOLD(R) assessment system (GOLD(R)) is a teacher rating system (authentic performance assessment) child observation tool designed to measure the on-going development and learning progress of children birth through kindergarten across various domains: social-emotional, physical, language, cognitive, literacy, mathematics, and English language acquisition. This article explores evidence for the reliability and validity of the information provided by GOLD(R) using two national samples (n1= 10,963, n2= 20,970). Support for the reliability and validity of scales scores based on teacher ratings is reported, including confirmatory factor analysis, classical and modern indexes of reliability, and inter-rater reliability statistics. In a separate study, concurrent validity was explored using a different sample of 3-and-4-year-olds (n = 1241). Accounting for teacher ratings and clustering effects, moderate associations were found between GOLD(R) scale scores and a direct assessment measure. Implications for teachers using the measure in the early childhood classroom and for future research are discussed. (author abstract)