This workbook, the third in a series of "Prevention Plus" publications, provides a step-by-step approach to assessing alcohol and other drug prevention programs at the school and community level. Program assessment is presented according to a four-step model: (1) goal and desired outcome identification; (2) process assessment; (3) outcome assessment; and (4) impact assessment. The workbook contains several major sections. The first two sections describe the logic of program assessment, the basic four-step approach to assessment, and the benefits and some of the costs and fears of program assessment and evaluation. The section on prevention describes basic concepts of prevention and discusses problems and recommendations in prevention programming and special considerations in evaluating prevention programs. The section on program assessment plans describes the plan for collecting information about program effectiveness and the degree of confidence with which the information can be interpreted. Pre-program assessment, post-program assessment, and other aspects of program assessment design are discussed. The next two sections on using this workbook provide: (1) an overview of the four-step worksheets and steps in preparing a report; and (2) two examples of program assessment using the worksheet modules. The next, and by far the longest, section is devoted to specific worksheets to be used in evaluating any of 50 types of activities that are commonly used in alcohol and other drug prevention programs. Examples are provided and directions are given for getting started on program assessment. The last section concerns assessment measures; it includes questionnaires and survey instruments that can be used to measure the program outcomes and the impact the reader hopes to achieve from local prevention programs. A list of clearinghouses, specialized information centers of national organizations, and Department of Education Regional Training Centers is included. (LLL)