Previous research has indicated that preschoolers identified for aggressive behavior would benefit from family, group, or individual therapy. However, there remains an important gap in the current literature regarding treatments for aggressive behavior based on the subtype of aggression. The purpose of this pilot study was to examine if 2 preapproved treatments, cognitive behavioral therapy (CBT) and interpersonal skills training (IST), administered to a convenience sample of 24 preschoolers who have been identified for aggressive behavior, were related to a reduction in 2 subtypes of aggressive behavior (proactive and reactive). Social learning theory, which states that aggression is a learned behavior, and aggression frustration theory, which states that aggression is the result of frustration, formed the theoretical foundation for the study. A quantitative two-way between-subjects analysis of variance design was used to analyze the relationship between the dependent variables (aggression, externalized behavior, and internalized behavior) and independent variables (type of aggression and type of treatment). The results indicated no significant change in behaviors regardless of aggression type, treatment, gender, race, or age. Further areas of research could include parental involvement and increase the amount of time the treatments are administered. This study contributes to social change by adding to the body of knowledge on early intervention in childhood aggression that will lead to more effective treatment by parents and educators of aggression in preschoolers and result in an enhanced preschool experience for children. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]