The effects of two data-utilization rules on spelling achievement were compared for an 11-year-old boy who had been diagnosed as learning disabled (LD). During instructional sessions, the boy was taught and measured on sets of difficult spelling words. Graphed data were analyzed using a concurrent schedule design whereby equivalent behaviors are treated simultaneously with different approaches to determine relative treatment effects. One treatment approach involved the following data-utilization rule: if the student's performance fell below the expected level on 3 consecutive days, the teacher made changes in the student's program. In the second treatment, the teacher made changes in the student's program every 5 to 10 days. Results indicated that, in the second data-utilization condition, the student's trend lines over a 6-week treatment period were superior to trend lines in the first data-utilization condition. (Author/CL)