Most people have 23 pairs of chromosomes; one set from the mother and one from the father. However, nondisjunction errors during meiosis can lead to a case of trisomy, where there are three rather than two chromosomes. Although such events are not uncommon, they are usually lethal, and account for a high proportion of spontaneous abortions. There…

Critiques Walker's article in this issue. Argues that Walker's data do not meet technical standards regarding individual placement tests for normative comparisons, interjudge reliability, or predictive validity, and therefore do not justify the use of the Gesell test to place children in developmental kindergarten or transitional first grade. (GLR)