Teaching sight words to students with mental retardation and learning disabilities: Constant time delay versus interspersal of known items

This study compared the efficacy and efficiency of using constant time delay (CTD) with interspersal of known items (IKI) paired with an error correction technique to teach sight words to students with mild mental retardation and learning disabilities. Time delay is a technique that transfers stimulus control from a controlling prompt (a prompt that results in correct task performance) to the discriminative stimulus (stimulus presented before a response can occur) by delaying the presentation of the prompt after the stimulus has been presented. During the initial trial, the delay between prompt and stimulus is at 0-seconds; during all other trials the delay is fixed at 4-seconds. Interspersal of known items is a method of sequencing unknown or target words among known words. Two sessions were provided each day in the classroom, one with constant time delay technique and the other with interspersal of known items as the training technique. The parallel treatment design was used to assess the efficacy and efficiency of the two strategies. The results indicate that both techniques were effective for students with LD. Constant time delay was significantly more effective than interspersal of known items for the students with MMR. Based on both the number of minutes of instructional time and the number of sessions through criterion, the constant time delay procedure was more efficient for students with MMR. However, the interspersal of known items technique was more efficient in terms of percentage of errors and rate of correct responses for both students with MMR and LD.