Over 200 million children under the age of 5 are not fulfilling their developmental potential due to poverty, poor health, and lack of cognitive stimulation. Experiences in early childhood have long term-effects on brain development and thus the cognitive and social-emotional skills that promote children's school success. Further, early childhood development is linked longitudinally to children's educational outcomes in low- and middle-income (LAMI) contexts. The present study seeks to explore the impacts of an early responsive stimulation intervention on children's behavior problems and social skills at age four in rural Pakistan. The authors further examined whether home environment quality mediated the effects of the intervention on children's behavior problems and social skills. The study included 1302 children and their primary caregivers who were enrolled in the Pakistan Early Child Development Scale-Up (PEDS) Trial and followed up at age four. The current study is a four-year-old follow-up of the PEDS trial, a 2x2 factorial intervention with responsive stimulation and enhanced nutrition interventions. Comprehensive child and maternal assessments were conducted during a three-hour home visit. This study demonstrates the value of an early responsive stimulation intervention on children's social-emotional skills in LAMI contexts. Further, it extends previous literature by highlighting the importance of home environment quality in mediation associations between the intervention and children's development. Two tables and a figure are appended.