The nearly 1 million young children with special needs are regularly being assessed around the country for different purposes. Although a variety of assessment tools are being used for these purposes, many have not been validated for use with these children. Much more information is needed about assessments and children with special needs, such as what tools are being used by what kind of professionals to make what kind of decisions. Assessment for eligibility determines whether a young child will have access to services provided under the IDEA. It is unknown to what extent these critical decisions are being made consistent with recommended assessment practices and whether poor assessment practices are leading to inappropriate denial of service. The increasing call for accountability for programs serving young children, including those with special needs, means that even more assessment will be occurring in the future. Yet the assessment tools available are often insufficiently vetted for use as accountability instruments, and they are difficult to use in standardized ways if children have special needs, and they focus inappropriately on discrete skills rather than functional capacity in daily life. Until more information about assessment use is available and better measures are developed, extreme caution is critical in reaching conclusions about the status and progress of young children with special needs. The potential negative consequences of poor measurement in the newest area of assessment, accountability, are especially serious. Concluding that programs serving young children with special needs are not effective based on flawed assessment data could lead to denying the next generation of children and families the interventions they need. Conversely, good assessment practices can be the key to improving the full range of services for young children with special needs: screening, identification, intervention services, and instruction. Good assessment practices will require investing in new assessment tools and creating systems that ensure practitioners are using the tools in accordance with the well-articulated set of professional standards and recommendations that already exist.