Drowning is a leading cause of unintentional death among children worldwide. Children with autism spectrum disorder (ASD) are at higher risk for incidents of drowning then their non-disabled peers. Mastering water safety skills, such as underwater submersion, has been associated with a decreased risk for incidents of drowning. Using a combined multiple-baseline and changing-criterion design, this study examined the effects of a behavioral treatment package consisting of shaping, prompting, and positive reinforcement utilized to teach three young children to demonstrate underwater submersion during weekly swimming lessons. During baseline, none of the participants submerged their head underwater despite previous modeling and instruction. Following the implementation of the behavioral treatment package, all three participants submerged their entire head underwater. Each participant maintained this skill following instruction and later developed more advanced swimming abilities utilizing the mastered skill of underwater submersion.