The development of young children's counting has been extensively researched, yet detailed studies that examine development over multiple years are curiously absent from the literature. This research examined 15 preschoolers' (ages 3-4) use of number words as they engaged in two counting tasks, an oral counting task and counting a collection of 31 pennies, at four time points over 2 years. This study highlights patterns in the development of a number word list for the 15 children and presents three cases that illustrate the ways in which development varied for different children over time. Findings indicate that children demonstrated emerging understandings of the structure of the number sequence within the teen numbers and beyond before consistently using the conventional, "correct" sequence. Implications for research and instruction include how assessment of mathematical tasks are conducted and coded to capture children's important understandings beyond accuracy as well as how the development of counting and mathematical practices are viewed.