Measurement in early care and education, and early intervention, particularly, continues to be dominated by the use of conventional, norm-referenced testing practices to the detriment of young children. Conventional tests have been neither developed for nor field-validated on infants, toddlers, and preschoolers with developmental disabilities. Thus, contrary to professional wisdom in the fields, conventional tests have no evidence-base for use in early childhood intervention. Nevertheless, the accountability movement in education embodied in No Child Left Behind legislation continues to promote the use of conventional tests, which yield distorted results for young children with special needs. It is long overdue for our interdisciplinary fields to abandon decontextualized testing practices and to champion the use of measurement techniques that capture authentic portraits of the naturally occurring competencies of young exceptional children in everyday settings and routines—the natural developmental ecology for children. In this article, we present the “authentic assessment alternative” to the mismeasure of young children. We review the purposes for assessment in early childhood intervention; issues related to conventional testing; 8 standards for professional “best practices”; a rationale and examples of the process and methods for authentic assessment; and guidepoints for implementing authentic assessment in action.