The assessment of young children in early childhood special education is a central area of educational practice. The results of child assessments often have significant implications for young children, their families, and the programs that serve them, including eligibility for special education services, instructional planning, and documentation of child outcomes. The array of early childhood assessment types and purposes can be challenging to disentangle at the practitioner and policy level. At this time, different types of assessment tools (e.g., norm-referenced and criterion-referenced) are being used to document the development and learning of children and little attention has been paid to the parallel information produced from different assessment types. The purpose of this study is to compare the assessment results from two types of developmental instruments commonly used (Assessment, Evaluation, and Programming System Second Edition [AEPS 2nd ed.] and Battelle Developmental Inventory II [BDI-2]) to determine their congruence in determining a child's developmental status (e.g., "on track" or delayed). Results indicate substantive difference between the two measures highlighting the potential for mismeasurement and misinterpretation of child assessment data. Implications for policy and practice are discussed. (author abstract)