Recent research has found that school readiness is a multi-faceted construct associated with academic ability as well as social-emotional skills, executive functioning, demographic, environmental, and other variables. However, most research assesses school readiness through children’s performance on discrete, typically standardized tasks, which may not be representative of the skills and behaviors children display at school day-to-day. The present study utilized a new measure, the Teacher School Readiness Scale (TSRS), to examine teachers’ perceptions of kindergartners’ school readiness. Drawing from a sample of 70 kindergarten students attending private schools in a semi-urban area, this study used exploratory factor analysis, bivariate correlation, and multiple linear regression to analyze how students’ demonstrated classroom skills and behaviors relate to one another as well as to students’ global school readiness. The study then used multiple linear regression to examine how teacher-rated school readiness relates to children’s performance on standardized performance tasks and rating scales representative of those typically used in school readiness literature. Factor analysis separated items on the TSRS into factors of Academic Understanding and Social Interactions, which correlated significantly with one another and predicted global readiness ratings. TSRS factor scores were not significantly correlated with performance measures of the same constructs. From five composite variables representing children’s academic, social-emotional, and executive functioning skills, only teacher-completed rating scales of executive functioning skills significantly predicted children’s overall school readiness. Results suggest poor ecological validity of traditional school readiness research methods and indicate need for inclusion of teacher-report measures in future school readiness studies.