This paper describes a research study that assessed young children with a low incidence disability, specifically Cri-du-Chat Syndrome (CDSC). A description of the concerns of assessing individuals with low incidence disabilities is described. Parent reports (using the Development Observation Checklist System) on the functioning of their children are analyzed and compared to data collected from more formal assessment (specifically, the Battelle Developmental Inventory). Data collected from parent report and formal assessments are included. A result of the analysis shows that parents' reports are congruent with formal assessment data. (Contains 3 tables.)