There is a dearth of research available on child services in the community mental health setting in the fields of psychology and counseling. The purpose of this study was to conduct an experimental evaluation of university-based play therapy clinical services with children aged 3 to 10 years old and to explore dimensions of the effectiveness of child-centered play therapy (CCPT) with children. This study examined real-life clinical services to the largest number of child participants in decades of mental health research, especially in the field of play therapy. Archival data from cases of 364 children served through a university-based play therapy clinic in the southwestern United States was examined. The effectiveness of child-centered play therapy (CCPT) was measures by a decrease in a child's behavioral problems perceived by a parent/guardian measured by scores of the Internalizing Problems, Externalizing Problems and Total Problems on the Child Behavioral Checklist (CBCL) and a reduction of parent-child relationship stress manifested in the Child Domain, Parent Domain and Total Stress Score on the Parenting Stress Index (PSI). Data from pretest and posttest was gathered for use in the analysis. Independent samples t-test, repeated measures analysis of variance, and ordinary least squares regression, including effect sizes, were utilized to detect the differences between groups and the treatment effects. After receiving individual CCPT, results of this study demonstrated statistically significant differences on overall CBCL and PSI measures, with the exception on Parent Domain. Additionally, findings highlighted the effectiveness of individual CCPT through demonstrated moderate to large effects over time (partial η2 = .097 to .201). Individual CCPT also revealed very large effects (η2 = .26 to .37) when specifically examined with participants who completed play therapy treatment. Further, statistically significant predictions were found on CBCL and PSI measures, with the exception on Total Problems. Termination and family relationship concern variables were found as strong contributors on predicting greater improvement. Based on the statistical, practical, and clinical significances, the primary contribution of this study is the fully exploration of child characteristics and effectiveness of play therapy for children who seek mental health services.