Progress monitoring measurement is increasingly needed in early childhood to inform practitioners when an intervention change is needed and as a tool for accomplishing individualization and improving results for individual children. The Early Communication Indicator (ECI) is such a measure for infants and toddlers, 6 to 42 months of age. A greater understanding of the ECI key skills (i.e., gestures, vocalizations, single- and multiple-word utterances) could lead to further improvements in the sensitivity and utility of the decisions made compared to ECIs composite total communication score. Thus, we examined the pattern of growth within and between the ECI's four foundational skills in a large sample of children served in Early Head Start. Results confirmed a unique pattern of growth and change within each skill trajectory in terms of (a) age at skill onset and (b) peaks in each trajectory defining an inflection point or change from acceleration to deceleration. Analyses using these inflection points as intercepts with before and after trajectory slopes in a test of an adjacent skills temporal ordering growth model indicated good fit. Implications of a continuum of foundational ECI skills to future validation and decision making utility of the measure are discussed.