Disruptive behavior disorders including Attention-Deficit/Hyperactivity Disorder (ADHD), Conduct Disorder (CD), and Oppositional Defiant Disorder (ODD), are listed among the most common reasons youth are referred for mental health services (Centers for Disease Control & Prevention [CDC], 2016b; Kazdin, Mazurick, Siegel, & 1994). Parent-Child Interaction Therapy (PCIT) is one intervention that has been found to reduce clinically significant levels of disruptive behavior. The purpose of the current study was to determine the form of change, typical change trajectory, and individual variation in change for disruptive behavior across the two phases of PCIT; the Child-Directed Interaction (CDI) and Parent-Directed Interaction (PDI) phases. In addition, the current study determined which child and caregiver characteristics were associated with variation in change across CDI and PDI. Participants included a total of 75 children in PCIT between the ages of 2 to 8 years. Children and their caregiver(s) attended PCIT weekly at a university-based, outpatient clinic. The Eyberg Child Behavior Inventory (ECBI) was completed at every treatment session to indicate the intensity of disruptive behavior. Child and caregiver characteristics including the caregiver and the child’s gender, the caregiver’s income and marital status, the caregiver’s relationship with the child, the number of caregivers in PCIT, the child’s primary diagnosis, and the child’s medication status, were obtained through medical record abstraction. Results indicated the form of change in disruptive behavior, as measured on the ECBI Intensity scale, was linear in CDI and curvilinear in PDI. The average trajectory indicated disruptive behavior decreased throughout PCIT treatment. The decrease in ECBI Intensity scores during CDI was statistically significant, as well as the variance in children’s ECBI Intensity scores at the beginning of PDI. Caregiver marital status significantly predicted the ECBI Intensity score, which was higher for the divorced or separated group at the first session of PDI than other groups. Caregiver type also significantly predicted the ECBI Intensity score. When the caregiver was a grandparent, the ECBI Intensity score was lowest at the first session of PDI. However, the change in the ECBI Intensity slope for the biological parent group was steeper in comparison when transitioning from CDI to PDI, and less steep throughout PDI, than the grandparent group. Number of caregivers also was a significant predictor, with more caregivers present in PCIT indicating a greater decrease in the ECBI Intensity score. Significant child characteristic predictors were diagnosis code and medication status. For a diagnosis of Other (e.g., Adjustment Disorder, Selective Mutism), the ECBI Intensity score at the intercept was less than the ODD; ADHD; and Other Specified/Unspecified Disruptive, Impulse-Control, and CD groups; and higher than the Autism Spectrum Disorder/Social Pragmatic Communication Disorder group. A medication status of combined (greater than one psychopharmacological medication prescribed) indicated a higher ECBI Intensity score at the intercept, in comparison to the other groups. There was also a steeper change in slope throughout PDI when the diagnosis was ADHD in comparison to the ASD/SCD group. Last, when the medication status was single (one psychopharmacological medication prescribed), the change in slope during CDI for the ECBI Intensity score was steeper than the combined medication group. In summary, findings indicated disruptive behavior decreased during PCIT. However, clinicians and families may expect a slight increase in disruptive behavior at the beginning of PDI, or to see a slower rate of change in behavior, before the rate of change eventually speeds up and disruptive behavior decreases. Clinicians may see differences in the rate of change during PCIT based on caregiver and child characteristics and should use this information to guide discussions with families in the future. Future research should be conducted to determine if results may be replicated across different participant groups. Future studies may also follow-up on the maintenance of treatment gains after completing PCIT based on differences in rate of change for various caregiver and child characteristics examined in the current study.