In 1986, Congress passed Public Law 99–457, which provided incentives for states to develop early childhood intervention programs for qualified infants and toddlers from birth through 2 years of age and their families. The law later became known as the Individuals With Disabilities Education Act (IDEA),1 and, with the 1997 amendments, the early intervention program became Part C of the Act. Part C of IDEA defines the terms “evaluation” and “assessment” as they relate to early intervention programs. “Evaluation” means procedures used to determine a child's initial and continuing eligibility for services. Eligibility criteria are defined by each state, but they typically include documentation of delay in one or more areas of development listed in the federal law, including cognitive, adaptive (self-help), physical (eg, gross and fine motor), communication, and social-emotional development. “Assessment” is defined as ongoing procedures to identify a child's strengths and needs, and the services required to meet those needs. This is the process of program planning. Evaluation requires what Kirshner and Guyatt referred to as a “discriminative index,” which distinguishes “between individuals or groups on an underlying dimension when no external criterion or gold standard is available for validating these measures.”2 Measures useful for determining a child's eligibility for services are those that can be used to differentiate between children who have developmental delays and children who do not have such delays.3 Discriminative measures include test items that distinguish between children of varying ages, such as stacking blocks or jumping down from a step. Although such information is can be useful for determining whether a child has a developmental delay, knowledge that a child can or cannot perform such test items often is not useful for program planning purposes. Program planning often requires identification of goals specific to an individual, particularly when intervention …