in notebooks, Post-it notes, and wall charts and used these documents to graph changes over time.

All of this documentation became “data” to think about, question, and argue with. Using these data, they could describe and discuss patterns of vegetation and the relationships among vegetation and animal life. With their maps, charts, and evolving field guide, they could raise questions about the evidence they’d gathered and what it meant. If they needed more evidence, they could design investigations to answer specific questions. When their maps of the schoolyard showed a different density of fall woody plants on one side, they collected more systematic evidence of the height of the trees, using handmade altimeters. They found, to their surprise, that the trees on one side of the yard were taller on average. With careful documentation of the height of the trees, the students generated questions about the causes of differential tree height. Was it due to differences in exposure to sunlight or water? Was it because there were different species of trees present? Or was it due to the age of the trees? These questions led to a detailed cataloging of species as well as an investigation of sunlight, ground temperature, and ground moisture. Good evidence led to more questions, which in turn led the students to generate more evidence.

The students in the two classes had many opportunities to reflect on their increasing knowledge as well as on the puzzles they encountered. In exploring the answer to the question of why the trees on one side of the yard were taller, the students were aware of the limitations of their evidence with respect to the age of the trees. When reporting on their findings after a fieldwork activity, they asked each other questions about the quality and reliability of the data they were collecting. Increasingly, they asked for evidence from one another when causal explanations were proposed.

As the field guide developed over the year, there were disagreements about classifications that needed to be resolved. The students became aware of occasional mistakes and paid attention to how these mistakes were corrected, as well as to how their ideas changed over time. The most obvious example of this was the shift in students’ thinking about the differences between weeds and flowers. The field guide became a “collective memory” for the group. Updates to the guide reminded everyone of how thinking can undergo significant change.