The main objective of this study was to assess whether training of private health providers and community sensitization on the importance of effective prompt care seeking and the need for referral could improve treatment of sick children in the private health sector in Uganda. Private providers were trained to diagnose and treat sick children according to the integrated community case management (iCCM) guidelines. In the control arm, routine services were offered. The outcomes were seeking care within 24 hours of onset of symptoms and appropriate case management for malaria, pneumonia, and diarrhea among children aged < 5 years. A total of 10,809 sick children (5,955 in the intervention arm and 4,854 in the control arm) presented for diagnosis and treatment. The percentage seeking care within 24 hours of onset of symptoms was 45.4% (95% CI 36.0-48.8) in the intervention arm versus 43.9% (95% CI 38.1-49.8) in the control arm (P = 0.04). Adherence to malaria rapid diagnostic test (mRDT) results was high, with 1,459 (94.3%) in the intervention arm versus 1,402 (83.0%) in the control arm (P = 0.04). Appropriate treatment of mRDT-positive children with artemisinin-based combination therapy was seen in 93.1% (95% CI 88.5-97.7) in the intervention arm versus 85.1% (95% CI 78.6-91.7) in the control arm (P = 0.03). Adherence to iCCM guidelines was very high: 89.1% of children with diarrhea in the intervention arm and 80.4% in the control arm were given oral rehydration salts and zinc (P = 0.01). Of the children with a respiratory rate > 40 breaths/minute, 1,596 (85.1%) in the intervention arm versus 104 (54.5%) in the control arm were given amoxicillin (P = 0.01). In conclusion, the intervention improved treatment of malaria, pneumonia, and diarrhea because of provider adherence to treatment guidelines. The policy implications of these findings are to initiate a dialogue at district and national levels on how to scale up the intervention in the private sector. NCT02450630 registered with ClinicalTrials.gov: May 9, 2015.