Calculation fluency weaknesses are a key characteristic of children with mathematics difficulties. The major aim of this dissertation was to uncover early predictors of calculation fluency weaknesses in second graders. Children's performance on number sense tasks in kindergarten along with general cognitive abilities, early literacy skills, and age were used in a block multiple regression analysis to predict calculation fluency in second grade (N = 198). When all of the variables were in the model, working memory, number knowledge, and number combinations were unique predictors of calculation fluency, with number combinations making the largest contribution. Hit rate analysis indicated that the number sense test in kindergarten ruled out the majority of the children who did not go on to have calculation fluency difficulties in second grade and positively identified about half of the children who went on to have fluency problems. The relation between reading fluency and calculation fluency was also examined. The correlation between the two skills was significant (r = 0.41). However, predictors of reading fluency differed from predictors of calculation fluency. Age, early literacy, working memory, and counting were unique and significant predictors of reading fluency, with early literacy making the largest single contribution. Working memory predicted both calculation and reading fluency. The results provide guidance for understanding predictors of calculation fluency and identifying children who might benefit from targeted interventions in mathematics. Early understanding of numerical magnitude representations and operations appear to play an important role in developing fluency in second grade. Examining children's errors and strategies provided insight into children's thinking about addition and subtraction and may aid in intervention planning. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]