We investigated Early Head Start home visitors' use of evidence-based practices and the efficacy of a web-based system to support these practices. Home visitors learned to use 3 evidence-based practices: (a) frequent assessment of children's early communication for screening and progress monitoring, (b) 2 home-based language-promoting interventions, and (c) data-based decision making in the use of the language-promoting intervention strategies. Two conditions were compared in a randomized control trial. Condition A involved the use of an online data collection system, training in data-based intervention decision making, and training in the evidenced-based language interventions. Condition B was the same as A plus additional web-based support (MOD: Making Online Decisions) linked to the children's expressive communication data. Results indicated that the expressive communication of children receiving MOD support grew significantly more than for children whose home visitors did not receive MOD support. Home visitors in both groups increased their monitoring of children in need of intervention. The dosage of the MOD intervention that children received varied within the group, and MOD home visitors reported high levels of implementation fidelity and satisfaction with the MOD system. Future research and implications for early intervention and home-visiting practices are discussed. (Contains 2 figures, 7 tables and 1 note.)