The general purpose of this study was to examine the effectiveness of constant time delay embedded in activities for teaching clothes name for preschool children with developmental disabilities. This study included four participants having Down syndrome with an age range of 43-46 months. All experimental sessions were conducted in one to one teaching style. All sessions were conducted in a classroom of the university unit where the participants are every day. A multiple probe design across behaviors and replicated across subjects was used. The dependent variable of the study was teaching the names of clothes name and the independent variable of the study was constant time delay procedure. There were, full probe, intervention, generalization and maintenance sessions in the study. The results concerning effectiveness revealed that all three participants acquired the target skills at criterion level. Furthermore, participants maintained acquired skills at criterion level and generalized acquired skills to another person at criterion level.