Institute for the Psychological Sciences This article presents case studies exploring two boys' uses of limit testing as a therapeutic tool in child-centered play therapy (CCPT). Both boys were referred for behavior that was abnormally disruptive for their age and setting, which was kindergarten in an elementary school that serves a very high poverty community and is accustomed to handling misbehavior. Data evidencing progress is provided as a reference point, while analysis is focused on conceptualization and mechanisms of change related to each child's use of limit testing in CCPT. The authors suggest that each boy used limit testing in CCPT to try out the therapeutic relationship as a stand-in for other relationships, to rethink relational expectations inside and outside of therapy, revisit unmet needs and meanings of early experiences, and change self-concept in ways that affected positive behavioral change.