Abstract
This study investigated the effects of interspersing known items during spelling instruction on new words for three mentally retarded students. Following a baseline consisting of the presentation of 10 test words per session, a multielement design was implemented. During interspersal training sessions, previously mastered words were presented alternately with each of 10 test words. During high-density reinforcement sessions, 10 test words were presented and additional reinforcement was provided for task-related behaviors. Throughout all conditions, test words were deleted and replaced after meeting a mastery criterion. Periodic retention tests were administered over mastered words and a cumulative retention test was administered at the end of the experiment. Results showed that high-density reinforcement did facilitate performance over baseline; however, intersperal training was superior to the other conditions in terms of both acquisition rate and short- and long-term retention. In addition, students preferred the interspersal condition when offered a choice.