We conducted a conceptual replication of Chi and Koeske (1983) and Gobbo and Chi's (1986) studies on children's knowledge acquisition. One hundred elementary school students (86 through 159 months of age, in school grades 1 through 7) were asked to recall information about Harry Potter and the Sorcerer's Stone, the first of the books in the Harry Potter series. A quantitative measure of expertise was derived by a summation of factor loadings that were drawn from a free response and trivia task and from the number of Harry Potter books and movies a child reported having read or watched. Different measures of expertise were strongly intercorrelated but were only moderately correlated with age or grade. Although there was a significant correlation between age or grade and knowledge acquisition and expertise, nearly every other measure that correlated with expertise maintained statistical significance, even when we controlled for age or grade. Furthermore, regardless of age or grade, children with higher knowledge acquisition and expertise scores sorted characters more cohesively, with more sophistication, and used more categories that require a deep understanding of the Harry Potter domain. These results reinforce the idea that expertise is an aspect of knowledge that can be separated from a child's level of cognitive development and is associated with a deeper and richer knowledge base.