to scientific fact, emerged over a long period of time. Change came about as the result of disagreement, the marshaling of systematic evidence, sustained investigation (which involved some surveying of students, adults, and local gardeners), and even the help of outside experts. Early on, some students proposed surveying the school and taking a vote, while others argued that there might well be scientific evidence they could find to establish a definitive answer. This turned out to be one of the most exciting periods of investigation during the year. Issues of confidence in one’s data, the reasonableness and persuasiveness of arguments, and the fruitfulness of certain lines of investigation became the primary focus of the later biodiversity conferences.

The Interrelated Nature of the Four Strands

While it is possible to separate the strands for the purpose of analysis, in practice the strands overlap. A specific task might function in multiple ways and be a part of multiple strands at once.

For example, in one of the monthly biodiversity conferences, a fifth-grade student, Cara, presented a chart showing plots of trees and calculations of tree heights on two different sides of the school. In showing the chart, Cara said that the tree group had determined how to measure the height of the trees using triangles and the Pythagorean theorem. But their calculations of tree height puzzled them and made them wonder if their data were accurate. A student from the audience asked if the difference might be related to sunlight because he had found in his experiment with wildflowers (growing under different conditions) that a certain wildflower grew faster and taller with more sunlight. In this brief exchange, the students were marshaling scientific explanations, using their own data as evidence, reflecting on their current understanding, and participating in authentic scientific practices as presenters and audience members. All four strands were actively in play.

It is important to emphasize that the different strands inform and enhance one another. They are mutually supportive so that students’ advances in one strand tend to leverage or promote advances in other strands. In the case of “Biodiversity in a City Schoolyard,” one can see this kind of synergy growing over the course of the investigation. Prior knowledge and understanding help the students as they begin observing and recording. Their different interests lead them in different directions in the early stages of fieldwork. The collection



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