Research has demonstrated that most-to-least (MTL) and least-to-most (LTM) prompting are effective in helping children with Autism Spectrum Disorders acquire a variety of new skills. However, when directly compared to one another, the efficiency and efficacy of the prompting procedures have been variable. The inconsistencies in the literature could be due to selecting prompt topographies that do not promote correct responding. To address this, the present study began by assessing different prompt topographies and then compared most-to-least (MTL) and least-to-most (LTM) prompt-fading with only prompt topographies that were potent enough to promote correct responding. The subsequent comparison of prompt-fading procedures revealed that MTL prompting was more effective and efficient than LTM prompting for all three participants. Further implications for practice and future research are discussed.Keywords Least-to-most . Most-to-least . Prompt . Prompting . Prompt-fading Children with autism spectrum disorders (ASDs) often require prompts to learn new behaviors and prompt-fading strategies to transfer stimulus control from the prompt to the naturally occurring discriminative stimuli. Two of the most commonly used prompt-fading procedures are most-to-least (MTL) and least-to-most (LTM) prompting (Libby et al., 2008). These procedures employ the same prompt topographies, including verbal, gestural, and physical prompts; however, they differ in the order in which the prompts are presented. MTL fading sequences order prompt topographies from the most intrusive (e.g., physical prompts) to the least intrusive (e.g., verbal). In LTM fading, prompt sequences are arranged in the opposite order.Both MTL and LTM prompting can effectively improve independent responding when compared to baseline levels of responding or control procedures (for a review, see Demchak 1990). A few studies have directly compared the effectiveness and efficiency of these two popular procedures (Libby et al. 2008;McConville et al. 1998;Walls 1981). In all of these studies with the exception of Libby et al. (2008), MTL and LTM procedures were similarly effective; however, efficiency outcomes were variable across participants and different measurements of efficiency.Of the aforementioned studies, Libby et al. (2008) conducted the most systematic analysis and comparison of MTL and LTM procedures. In the first experiment, a direct comparison of the procedures revealed that three of five participants met a mastery criterion with both procedures, whereas the other two participants only met a mastery criterion with the MTL procedure. Therefore, overall, the MTL procedure was more effective than the LTM procedure in this experiment. Efficiency data, on the other hand, were variable across dependent variables. The LTM procedure was more efficient for the three participants who met a criterion with this procedure when considering trials to criterion; however, the MTL procedure was more efficient for all participants when considering errors to criterion....