Early interventionists are accountable for the progress of children receiving their services. Technically adequate measures of the progress of individual children are needed. While the Early Communication Indicator (ECI) for infants and toddlers is one such measure, data to support its use are limited to a single research report. In this manuscript, findings from new samples are presented. Results indicated that growth parameters reported in the original ECI study were replicated generally and differences in growth were associated with differences in samples' and children's characteristics. Overall, more representative growth parameters were estimated for the larger composite sample of children. These findings demonstrate the feasibility and potential contribution of the ECI to assessing the progress of young children learning to communicate. (Contains 4 tables, 6 figures and 4 footnotes.)