Background: Progress monitoring is a vital strategy for evaluating skill development of young children receiving disability related services. Few effective progress monitoring tools exist for infants and toddlers, and research is needed to examine feasibility as they become available. Objective: The current study examined the implementation of an assessment protocol for monitoring the developmental progress of children receiving Early Intervention (EI) services. Specifically, we examined the implementation of Infant/Toddler Individual Growth and Development Indicators (I/T IGDIs). Our questions were related to fidelity of implementation by examining learning and using I/T IGDIs in practice; and coaching support utilized by practitioners. Method: Fifty practitioners serving 92 participating families received training and coaching support to reliably administer and score up to 4 I/T IGDI assessments and use them in practice. Quantitative and qualitative implementation data revealed interesting results. Results: Practitioners needed relatively few sessions in order to become certified to administer and score I/T IGDIs. On average, practitioners used 1-2 I/T IGDIs with each child and children received a range of assessment frequency with the communication indicator being the most frequently used and the social indicator least frequent. Both supports and challenges related to time, organizational supports and research/technology were identified. Conclusions: EI practitioners are skilled at learning new assessment strategies and implementing them into practice given adequate time, organizational support and coaching for implementation. Practitioners expressed concerns with I/T IGDI use given time limitations during their visits. In addition, the inclusion of research activities into the implementation process may produce unintended challenges.