Contents: Preface. Part I:Reasoning About Uncertainty and Variation. A. Masnick, D. Klahr, B. Morris, Separating Signal From Noise: Children’s Understanding of Error and Variability in Experimental Outcomes. C. Schunn, L. Saner, S. Kirschenbaum, J.G. Trafton, E.B. Littleton, Complex Visual Data Analysis, Uncertainty, and Representation. S. Trickett, J.G. Trafton, L. Saner, C. Schunn,“I Don’t Know What’s Going on There”: The Use of Spatial Transformations to Deal With and Resolve Uncertainty in Complex Visualizations. B. delMas, Y. Liu, Students’ Conceptual Understanding of the Standard Deviation. J. Garfield, B. delMas, B. Chance, Using Students’ Informal Notions of Variability to Develop an Understanding of Formal Measures of Variability. R. Lehrer, L. Schauble, Contrasting Emerging Conceptions of Distribution in Contexts of Error and Natural Variation. G. Leinhardt, J. Larreamendy-Joerns, Discussion of Part I: Variation in the Meaning and Learning of Variation. Part II:Statistical Reasoning and Data Analysis. K. Dunbar, J. Fugelsang, C. Stein, Do Naive Theories Ever Go Away? Using Brain and Behavior to Understand Changes in Concepts. P. Thompson, Y. Liu, L. Saldanha, Intricacies of Statistical Inference and Teachers’ Understandings of Them. K. McNeill, J. Krajcik, Middle School Students’ Use of Appropriate and Inappropriate Evidence in Writing Scientific Explanations. C. Konold, Designing a Data Analysis Tool for Learners. M. Lovet, N. Chang, Data-Analysis Skills: What and How Are Students Learning? D.L. Schwartz, D. Sears, J. Chang, Reconsidering Prior Knowledge. K. Koedinger, Discussion of Part II: Statistical Reasoning and Data Analysis. Part III: Learning From and Making Decisions With Data.D. Danks, Causal Learning From Observations and Manipulations. P. Sedlmeier, Statistical Reasoning: Valid Intuitions Put to Use. W.B. de Bruin, J. Downs, B. Fischhoff, Adolescents' Thinking About the Risks of Sexual Behaviors. M. Burrage, M. Epstein, P. Shah, Discussion of Part III: Learning From and Making Decisions About Data.