The proposed dissertation project will examine how a new preventive intervention, Recipe 4 Success, which was embedded within Early Head Start home visits, can enhance implementation quality, leading to greater improvements in parent and toddler functioning across multiple domains. The goal of this dissertation is to gain a deeper understanding of what comprises high-quality early childhood home visiting and identify ways to improve home visiting services so all families can benefit. This dissertation will consist of three distinct but related empirical studies, each with a unique aim: (1) assess heterogeneity among home visits and whether being randomly assigned to participate in Recipe 4 Success is associated with higher quality home visits, (2) examine whether the Recipe 4 Success curriculum will help mitigate the barriers associated with having a still-developing parent-home visitor working alliance, and (3) determine how implementation fidelity to the Recipe 4 Success curriculum and family enjoyment are related to one another and to gains in parent sensitivity and learning support and toddler self-regulation. (author abstract)