Representing students' thinking about nutrient cycling in ecosystems: bidimensional coding of a complex topic

This study addresses the question of how to represent students' thinking about a complex topic in a way that is most useful to guide curriculum development, instructional decisions, and assessment of student learning. The development of a coding scheme that represents students' ideas along two dimensions, compatibility with expert propositions and elaboration of ideas, is described and applied to the analysis of interviews with four pairs of urban fifth‐ and sixth‐grade students. Results indicate that decomposition is a linchpin concept for building an understanding of nutrient cycling, and that ideas which relate to children's natural framework theories provide a generative foundation for further learning. Finally, it is suggested that the elaboration dimension of the bidimensional coding scheme provides an indication of students' possession of valuable scientific habits of mind. © 1996 John Wiley & Sons, Inc.