Parents of children with ASD (N = 86; mean age 44.8 months; 67 boys) were randomized to either WHO Caregiver Skills Training (CST) delivered in public health settings in Italy or enhanced treatment-as-usual. Primary blinded outcomes were 3-months post-intervention change scores of autism severity and engagement during caregiver-child interaction. CST was highly acceptable to caregivers and feasibly delivered by trained local clinicians. Intention-to-treat analysis showed a large and significant effect on parent skills supporting joint engagement and a smaller significant effect on flow of interaction. Expected changes in child autism severity and joint engagement did not meet statistical significance. Analysis of secondary outcomes showed a significant effect on parenting stress, self-efficacy, and child gestures. Strategies to improve the effectiveness of CST are discussed.