Counting skills are foundational for young children to build number concepts in mathematics. Multitiered instruction that involves core instruction as well as supplemental interventions is implemented to support young children in the learning process and promote early intervention of basic skills. Researchers show that explicit instruction is successful in teaching students in preschool. More research needs to be conducted on brief explicit mathematic interventions that target the skill of counting and are supplemental to preschool mathematics core instruction. In this study, researchers examine the effects of using explicit instruction as an intervention to teach counting skills for four children who were at risk for mathematics difficulties or who received special education services for developmental delay in an inclusive preschool setting. The researchers find a functional relation for a 15-minute supplemental explicit intervention and counting skills. Implications of these findings are also discussed.