Research Findings: This study provides the first independent investigation of the second most widely used multidimensional assessment in Head Start--the Preschool Child Observation Record, Second Edition (COR-2). We conducted a comprehensive investigation into the validity of the COR-2 using data from all children in an urban school district's Head Start program (N = 4,071). Confirmatory factor analysis revealed a misfit between the 6 developer-defined categories and the data. Although exploratory analyses revealed a possible 4-factor solution, subsequent analyses indicated problems with this structure as well. Item response theory methods were used to determine whether there was support for the 5-point response scale of each item representing an appropriately sequenced set of skill points. Results indicated that nearly half of the COR-2 items had reversed or poorly spaced thresholds, suggesting potential problems with these items' functioning. Practice or Policy: Specific implications of the findings for the further development of the COR-2 in terms of its constructs and items as well as general implications for early childhood assessment are discussed.