The Child Behavior Scale (CBS) is a teacher-report instrument that was developed over a decade ago as an alternative to more costly methods for assessing children's behavior and peer relations in school contexts. This investigation was undertaken to clarify how well the CBS achieves its aims with a broader age spectrum of youth (6- to 13-year-olds). Investigative aims were to examine the basic psychometric properties of the CBS and evaluate the construct and criterion-related validity of the CBS's 6 subscales at each of 8 grade levels (Grades 1-8). These aims were examined in a longitudinal investigation with samples of children and their teachers, classmates, and parents. One sample (n = 396) was followed from 1st through 8th grade, and a second sample (n = 100) was recruited in 5th grade, combined with the initial sample, and followed through 8th grade. Results suggest that the majority of the CBS subscales provide trustworthy data about the behavioral and peer relational constructs that this instrument was designed to measure and that the CBS's range of application, or developmental purview as an assessment tool, spans the period from early childhood (age 5) through early adolescence (age 13). (Contains 5 tables, 1 figure, and 1 footnote.)