Background: This study evaluated a new prevention and early intervention parenting program: "Tuning in to Kids." The program aims to improve emotion socialization practices in parents of preschool children and is based on research evidence that parents' responses to, and coaching of, their children's emotions influence emotional and behavioral functioning in children. Methods: Two hundred and sixteen primary caregiver parents of children aged 4.0-5.11 years were randomized into an intervention or waitlist control group. Parents in the intervention condition attended a 6-session group parenting program plus two booster sessions. Assessment occurred pre-intervention, post-intervention and at six-month follow-up. Questionnaires assessed parent emotion awareness and regulation, parent beliefs and practices of emotion socialization (emotion dismissing, emotion coaching, empathy) and child behavior (parent and teacher report). Observation of emotion socialization practices and child emotional knowledge was conducted pre-intervention and at follow-up with 161 parent-child dyads. Results: Parents in the intervention condition reported significant improvements in their own emotion awareness and regulation, increases in emotion coaching, and decreases in emotionally dismissive beliefs and behaviors. There were increases in parents' observed use of emotion labels and discussion of causes and consequences of emotions with their children. Child emotional knowledge improved, and reductions in child behavior problems were reported by parents and teachers. Conclusions: This study provides support for the efficacy of a parenting intervention targeting parent emotion socialization practices that lead to improved child emotional knowledge and behavior. This preventative intervention targeting parents' own emotion awareness and regulation, as well as emotional communication in parent-child relationships, is a promising addition to available parenting programs. (Contains 1 figure and 2 tables.)