The proposed study will evaluate, via a randomized controlled trial, the incremental utility of I-PCIT for disruptive behavioral problems in traditionally underserved young children with developmental delay (DD) from predominantly economically disadvantaged and ethnic and racial minority backgrounds. Specifically, the investigators are interested in the impact of I-PCIT on child disruptive behavior problems, parenting practices, parental distress, and pre-academic skills relative to traditional referrals as usual (RAU) among youth aging out of Part C EI services and transitioning from home-based family services to school-based special education services. A secondary goal is to evaluate potential moderators and mediators that explain under which circumstances, for whom, and through which pathways I-PCIT is most effective for young children with DD. Our primary aims are (1) to evaluate the immediate and one-year impact of I-PCIT on (1a) disruptive behavior problems in young children with DD, as well as (1b) parenting practices and (1c) parental distress in parents of young children with DD; (2) to evaluate the impact of I-PCIT on pre-academic skills among young children with DD; and (3) to evaluate (3a) family retention, (3b) engagement, and (3c) satisfaction associated with I-PCIT in young children with DD. Our secondary aim is to examine potential moderators and mediators of response to I-PCIT for disruptive behavior problems in young children with DD. Specifically, the investigators are interested in the extent to which technological literacy and access (4a) moderate I-PCIT efficacy, such that I-PCIT efficacy will be weaker among families with poorer technological literacy and/or access, and the extent to which traditional barriers to care (4b) moderate I-PCIT efficacy, such that the incremental efficacy of I-PCIT over RAU will be strongest among families with geographic, transportation and/or childcare obstacles to in-person services. Finally, the investigators hypothesize that I-PCIT will yield changes in child behavior and pre-academic skills indirectly through direct effects on parenting practices (4c). Specifically, changes in parental consistency, warmth, follow-through, and effective discipline will mediate observed I-PCIT efficacy, such that these treatment-related parenting changes will account for observed differences in child disruptive behavior problems and pre-academic skills.