How early is too early? As testing has grown more widespread in recent decades, important issues have arisen concerning how to ensure that early childhood testing is used appropriately and with positive educational benefits. Actually, this kind of testing has been happening for a long time. Testing young children became a frequent practice when educational testing first became popular in the early 1900s. By the late 1980s, 19 states required mandatory kindergarten screening tests. However, while noting the usefulness of some types of early childhood testing, researchers have also pointed out that tests tend to be less reliable at very early ages. The cautions of testing researchers, combined with their own experiences, have resulted in most states delaying the testing of children in public schools until the 3rd grade. The 2001 "No Child Left Behind Act" requires state testing in mathematics, reading/language arts, and science, starting in third grade. Nonetheless, a number of private schools, including Catholic schools, do require entering kindergartners to pass a test as part of their admission requirements. Some public elementary schools also continue to test very young children and use the results for key decisions, such as entry into a gifted public school. (Contains a list of 6 resources.) [This article was produced by the Center for Assessment and Evaluation of Student Learning (CAESL) at WestEd.]