Literature suggests that traumatized children exhibit a type of play that is distinct from the play behaviors of other children (Terr, 1983). The purpose of this study was the development of an instrument designed to detect differences in the play therapy behaviors of children with a history of trauma versus children with no known history of trauma.The study consisted of two phases; the instrument development and pilot study phases. The researcher followed Hill's (1991) guidelines for instrument development. The scale was designed so that raters could rate a child's behavior, via videotaped play therapy sessions, at five minute intervals. The scale consisted of the following domains: Intense Play, Repetitive Play, Play Disruptions, Avoidant Play Behavior, and Negative Affect. The Average Trauma Play Scale Score is an average of scores across these domains.During the pilot study phase, the researcher evaluated the scale in terms of reliability, face validity, and discriminant validity. Subjects were twelve children; six had a history of trauma and six had no known trauma history. Five trained raters rated eight consecutive videotaped play therapy sessions for each participant. One-way and repeated measures analysis of variance statistics, including effect sizes, were used to detect differences between the groups.Percentage agreement and correlational estimates of interrater reliability suggest that raters are able to acheive consensus and consistency in their ratings. Quantitative and qualitative feedback from experts in the field of play therapy provide strong support for the face validity of the scale. Statistical analyses indicate that the Trauma Play Scale has a high degree of discriminant validity. Traumatized children scored higher on the Trauma Play Scale than nontraumatized children, as expected. Effect size estimates indicate strong relationships between participants' trauma history status and their Average Trauma Play Scale scores. In post-hoc analyses, the Repetitive Play Domain was omitted from the aggregate score; this analysis uncovered statistically significant differences between the two groups.ii