Early math skills predict later achievement for young children; thus, it is important to expand what is known about how to support preschool children's development of these skills. While there has been some research on interventions, including those using systemic instruction, to teach math skills to preschoolers, there is a need for additional research to expand the field's knowledge about what works, for whom, and under what conditions. I used an experimental single case design--a multiple probe design across behaviors, replicated across children--to determine if there was a functional relation between the demonstration-practice procedure embedded in researcher-created books and preschoolers' acquisition of three early math skills. A functional relation was found for each participant, with some modifications needed for one participant. This is consistent with existing research that suggests systematic instruction is an effective approach for supporting preschoolers in acquiring early math skills. Additional research is needed to determine how best to choose skills to target for instruction, how to account for the relationship between math and other domains of development when teaching early math skills to preschoolers, and how to ensure interventions can be implemented with fidelity and adaptability.