Co-Principal Investigators. Any opinions, findings, conclusions or recommendations expressed here are those of the authors and do not necessarily reflect the views of the National Science Foundation. Models and Moves Extensive research on students ’ understanding of science has documented persistent shortfalls at all ages. One way to account for students ’ difficulties is to consider the particular challenges posed by individual science concepts. This article offers an alternative view. We argue that students’ difficulties in large part reflect unfamiliarity with a small number of causal modeling styles charac-teristic of received scientific models. These include, for instance, explaining surface phenomena with an underlying mechanism, relying on constraint-system explanations as in Ohm’s law, includ-ing probabilistic elements as in chaos theory, and acknowledging causal webs and self-organizing systems as in ecologies--in sum, aspects of “complex causality. ” A further barrier to understanding is students ’ unfamiliarity with epistemic moves that might challenge their initial explanations, such as looking for missing links in a causal story or putting a model at risk. The article offers a frame-work for classifying aspects of complex causality in modeling and for supporting epistemic moves. Empirical research both from the literature and our own work is presented in support of the framework, including evidence that instruction based on causal models and epistemic moves enhances students ’ understanding of science concepts. 2

This paper is based on the results of research carried out during the first year and a half of the Understandings of Consequence Project. We are continuing to research and develop the ideas presented here. If you have feedback for us or would like to keep in touch with developments on the project, please check our website at http://pzweb.harvard.edu/Research/UnderCon.htm or send us an email at Tina_Grotzer @PZ.Harvard.Edu.

This paper is based on the results of research carried out during the first year of the Understandings of Consequence Project. We are continuing to research and develop the ideas presented here. If you have feedback for us or would like to keep in touch with developments on the project, please check our website at http://pzweb.harvard.edu/Research/UnderCon.htm or send us an email at Belinda @ PZ.Harvard.Edu or Tina _Grotzer@PZ.Harvard.Edu. This paper is based upon the work of Understandings of Consequence Project, which is supported by the National Science Foundation, Grant No. REC-9725502 to Tina Grotzer and David Perkins, Co-Principal Investigators. Any opinions, findings, conclusions or recommendations expressed here are those of the authors and do not necessarily reflect the views of the National Science Foundation. Acknowledgments We'd like to express our appreciation to the teachers and students at the Fox Hill Elementary School and the Pine Glen Elementary School in Burlington, MA for their participation in the research study outlined here. We also appreciate the support of Nora Sabelli, our program officer at the National Science Foundation. 1