The conceptual basis for using individual expectancy scores as a means for determining the success of instruction is presented. An expected gain score is computed for each student, based on a pretest score. The assumption is made that without a change in the learning environment the student will continue to gain at his previous average rate. The data are displayed in an achievement idiograph, which shows individual grade placement based on the pretest, expectancy score, and posttest placement. Data can be used at the individual student level by classroom teachers or aggregated by classroom, school, or district to serve the needs of other decision-makers. Less than expected gain can serve to quickly draw attention to areas of weakness in the curriculum; more than expected gain can be considered as "success." Idiographic analysis eliminates the necessity for control groups and historical data as means for assessing program success. (Author/KM)