This study described the development of the "Social Skills Improvement System Social Emotional Learning Edition Rating Forms" (SSIS SEL RF) for teachers, parents, and students. This new multirater assessment is a reconfiguration of the SSIS Rating Scales items inspired by the CASEL Social Emotional Competency framework. The internal structure and score reliability estimates were examined across three raters for a common sample of more than 200 individual children ages 3 to 18 years. Confirmatory factor analyses tested against the CASEL five-dimensional SEL theoretical model demonstrated adequate fit for the SSIS SEL Parent and Student RFs and mediocre fit of the Teacher RF. Internal consistency, test-retest, and interrater reliability estimates for scores on each of the SSIS SEL RFs all met or exceeded acceptable criteria. Thus, researchers and practitioners interested in measuring the social-emotional behavior of children ages 3 to 18 can expect reliable scores and structurally meaningful behavior content within the Collaborative on Academic Social Emotional Learning (CASEL) SEL competency framework. Limitations to the present findings and suggestions for future research conclude the report.