Chapter 1 Introduction to Special Issue: Investigating Part icipant Structures in the Context of Science Instruction; Chapter 2 The Teacher as Part ner: Exploring Part icipant Structures, Symmetry, and Identity Work in Scaffolding, Iris Tabak, Eric Baumgartner; Chapter 3 Dialogic Activity Structures for Project-Based Learning Environments, Joseph L. Polman; Chapter 4 Power in the Classroom: How the Classroom Environment Shapes Students' Relationships With Each Other and With Concepts, Lindsay L. Cornelius, Leslie Rupert Herrenkohl;