Programs serving infants and toddlers are expected to use child data to inform decisions about intervention services; however, few tools exist to support these efforts. The Making Online Decisions (MOD) system is an adaptive intervention that guides early educators' data-based intervention decision making for infants and toddlers at risk for language delay. Using a cluster randomized design to test the effect of the MOD, home visitors (HVs) were assigned to either use the MOD or not across 13 Early Head Start programs. Both groups used the Early Communication Indicator (ECI) for progress monitoring and a parent-mediated language promotion intervention. Children from both groups demonstrated significant growth in expressive communication. However, children whose HVs fully implemented the MOD grew significantly more than the group that did not use the MOD, even after statistically controlling for parent and HV variables. Implications for designing effective and usable systems to promote the use of data-based decision-making practices by infant-toddler service providers are discussed, as well as limitations of the current study. (author abstract)