Patterns are a pervasive and important, but understudied, component of early mathematics knowledge. In a series of three studies, we explored (a) growth in children's pattern knowledge over the pre-K year (N = 65), (b) the frequency of pattern activities reported by parents (n = 20) and teachers (n = 5) relative to other mathematical activities, and (c) changes in 4-year-old children's pattern knowledge after brief experience generating or receiving explanations on patterns (N = 124). Together, these studies illustrate the types of experiences preschool children are receiving with patterns and how their pattern knowledge changes over time and in response to explanation. Young children are able to succeed on a more sophisticated pattern activity than they are frequently encouraged to do at home or at school. (author abstract)