This report documents the reliability and validity of scores on the Preschool-Wide Evaluation Tool (PreSET), an assessment used to measure program-wide implementation of the universal level of positive behavior interventions and support (PBIS) in early childhood settings. Initial analyses of descriptive statistics, item, subscale, and total correlations and tests of internal consistency reveal that the PreSET meets or exceeds basic psychometric criteria for measurement tools used in research. The PreSET had strong subscale intercorrelations, high interobserver agreement, positive correlations to conceptually related subscales on the Teaching Pyramid Observation Tool, and sensitivity to implementation change. Overall, the PreSET demonstrates strong promise as a tool that generates reliable and valid scores to use in the assessment of program-wide implementation of universal PBIS in early learning environments.