Low income male preschoolers with externalizing behaviors have continued behavior issues throughout elementary school, middle school, high school, and into adulthood and create stress for their teachers. Because of this, it is important to detect externalizing behaviors early and implement an appropriate intervention. A single subject reversal design was used to examine the effects of child-centered play therapy (CCPT) on the externalizing behaviors of five low income male preschoolers during group instructional time and center time who scored the highest on the Externalizing Subscale of the Child Behavior Checklist/Caregiver-Teacher Report Form for Ages 1½ - 5 (C-TRF 1.5-5; Achenbach & Roscorla, 2001). These five children were observed and assessed twice a week on the Externalizing Subscale of the C-TRF by two blind observers. The child with the highest score on the C-TRF 1.5-5 (Student A) completed the reversal design, which included 21 thirty-minute play therapy sessions. The results of this study showed a functional relation between CCPT and externalizing behaviors with this child. The study also indicated that as this child began the intervention and his externalizing behaviors decreased, the other four male students’ externalizing behaviors decreased as well.