Discussed in a paper which was presented at the 1974 Annual Meeting of the American Educational Research Association are diagnostic procedures for instructional planning to be used with learning disabled elementary school children handicapped in the area of mathematics. Traditional diagnostic approaches such as intelligence tests are criticized. Offered is the engineering model of learning disabilities which provides for observation of a child's learning behaviors in an environmentally normal minisituation. Diagnosis of the child's functioning in mathematics is said to involve finding out how much the child knows in a given curriculum sequence, how the child learns new material, and how learning rate changes as a function of the child's environment. Explained is the core diagnostic procedure which examines changes in learning of five addition problems as a result of three types of feedback: acknowledgement of correct and incorrect responses, social praise for correct responses, and tangible reinforcement (tokens) for correct response. Additional modifications are given to include use of soft reprimands for incorrect responses, tokens in a response cost format, and behavior charting by the child. Advised for overcoming perceptual difficulties are modification of stimulus material such as using larger print. Suggestions are given for evaluating preferred learning modalities (visual or auditory), for determining difficulty levels through varying presentations of five addition problems, and for finding the optimum amount of over learning necessary for retention of material. Noted is the predictive relationship of the core procedure with school achievement. (MC)