Now at middle age, the field of Early Childhood Intervention (ECI) and its professionals have demonstrated a unique capacity to develop their own practice-based evidence (PBE) and professional standards to forge solutions to challenging professional practice dilemmas. This innovative capacity is no more evident than in designing and implementing individualized linkages among assessment/instruction/progress evaluation for all children, particularly those with delays and disabilities. In this article, the authors advocate for the overarching purpose of assessment in ECI - to identify instructional targets and to plan beneficial programs for young children with special needs in inclusive, natural environments. The authors highlight major developments that have changed their professional practices since the passage of PL 99-457; PBE that supports and promotes these practices and the linkage among assessment, instruction, and progress evaluation; and critical issues for future policy, practice, and research. (author abstract)