This report summarizes a project to develop computational estimation materials for students in grades 6, 7, and 8. In chapter 1, the need for estimation skills is discussed and the goals of the project are stated: to develop a carefully sequenced set of lessons, activities, and maintenance work on estimation with whole numbers, fractions, decimals, and percent; to implement the program in grades 6, 7, and 8; and to evaluate the effects of the program on achievement in terms of skill in estimation and the types of processes employed. The second chapter describes the guidelines, issues, components, and pacing of the program. In chapters 3 and 4, findings from the evaluation of the pilot materials are presented, while chapter 5 describes the revision process. Seven appendices contain the pacing guide for the pilot materials; the attitude questionnaire and results; the mental computation tests and results; the computational estimation test, acceptable intervals, and results; the midyear test and results; a summary of the interview packet; forms used to evaluate the instructional materials; and a list of presentations made to disseminate project materials. (MNS)