If the major educational objective of classifying children into restricted range classroom environments is greater provision for individual differences--and given that there is no clear-cut evidence indicating that this object has been realized--then one is compelled to entertain the conclusion that ability grouping, as presently implemented, has failed to establish its merit as a sound instructional policy. Despite its increasing popularity, there is a notable lack of empirical evidence to support the use of ability grouping as an instrumental arrangement in public schools. Data from a close examination of studies ranging from those done in the Plainfield, New Jersey school system, the court findings in the Hobson vs. Hanson case in Washington, D.C., plus data drawn from numerous earlier studies by eminent social scientists further reveal ability grouping as a questionable practice. Taken as a whole the data indicate that grouping on the basis of standardized measures of achievement or aptitude tends to systematically separate children along ethnic and socio-economic composition of classes that are formed on the basis of the ability grouping rule of organization. (Author/JM)