Relationship-based intervention programs are increasingly being implemented as a way to enhance parent-child interaction quality. In this meta-analytic review, we examined the effectiveness of 19 recent relationship-based interventions serving socioeconomically disadvantaged families with infants and toddlers (N = 6,807). This review specifically focused on intervention effectiveness in terms of improving supportive parenting behaviors, as measured by observational assessments of dyadic parent-child interactions. Meta-analytic results indicated significant, yet modest, effectiveness across all interventions (d = .23). Intervention characteristics such as participant randomization, breadth of intervention services offered, duration, child age at the start of the intervention, professional qualifications of the intervenor, and type of play task used during assessment were tested as possible moderators of effectiveness. Significant differences in effectiveness were found between randomized and nonrandomized interventions. Within the subsample of randomized interventions, programs that were shorter in duration, that provided direct services to the parent-child dyad, used intervenors with professional qualifications, and assessed parent-child interactions with free-play tasks were the most effective, highlighting important considerations for designing effective intervention protocol tailored to the needs of this high-risk population.