A scale was developed for judging the relative value of various media in teaching children. Posttest scores were partitioned into several components: error, prior knowledge, guessing, and gain from the learning exercise. By estimating the amounts of prior knowledge, guessing, and error, and then subtracting these from the total score, an index of effectiveness emerges. The resulting index has been applied as a selection criterion for multiple choice questions generated to measure objectives of instructional films. The index figure for each question was used to assign or verify assignment of grade, age, and achievement levels for the question. A high learning index value indicated a good match between question, media, and respondent. An average of these positive question index values then serves as an index of a given medium's effectiveness. The indexes from several media on the same subject matter would allow some comparison. Adding the results of observed attention spans, vocabulary levels, curriculum classes, and subject descriptors to the index value provides a profile of a given medium. This profile can then serve to indicate the medium's suitability for a given child, a given content unit, or a given level of skill development. (Author/JK)