When counting, the final word used to tag the final item in a set represents the cardinality, or total number, of the set. Understanding of this concept serves as a foundation for children's basic mathematical skills, such as arithmetic. However, little is known about how variations in the early learning environment affect children's understanding of this important concept. The current study examined the effects of the representational status of to-be-counted items on preschoolers' understanding of cardinality. Children (M age = 3 years, 6 months) were randomly assigned to receive counting practice with either physical objects or pictures over five practice sessions. Children's counting skill and understanding of cardinality were assessed at pretest and posttest. Results revealed that only children in the picture condition increased their understanding of cardinality from pretest to posttest. These findings suggest that small variations in the materials children use during counting practice can affect what they learn from that practice. Specifically, results suggest that picture books are better than physical objects at supporting children's understanding of cardinality.