the reading of expository texts. When it wasn’t clear whether a plant was the same as the one shown in the guidebook, students found other books or materials with information on the same plant. This, in turn, prompted the students to find additional information as they assembled clues: Where is the plant usually found? When does it typically bloom? How tall is it?

Cataloging the animals in the schoolyard was particularly challenging. How could they tell whether they were seeing two different squirrels or the same squirrel twice? Long discussions ensued. Mr. Walker explained that what practicing biologists do to identify particular animals is to put some kind of identifying device on them. This might entail capturing and perhaps even anesthetizing the animal. They might put a colored band on a leg or sometimes a spot of indelible paint (e.g., a green dot on the left rear foot for one squirrel and a red dot on the left rear foot for another squirrel). This, of course, would not be possible in their schoolyard. But, he told them, not all identification requires intervention. Whale biologists, for example, rely on photographs of whales, identifying individuals by the visible pattern of whale lice on their rear flukes.

After much discussion, during which different proposals were considered, the students decided that they could do something similar to what whale biologists do. After a period of observation, they asked if anyone had noticed squirrels with different characteristics—scraggly tails or bushy tails, squirrels with tails that are darker or lighter than their body fur, black versus brown fur, scars or bare patches, etc. The students made drawings, took photographs, and then attempted to record observations of particular individuals or species, according to these characteristics. From there, the students were able to develop reasonably reliable category systems, based on which features were most diagnostic in telling one squirrel from another.

From their initial observations, readings, and collections, the students decided to map their areas more carefully. This interest in more systematic sampling grew out of a lengthy discussion in one of the monthly biodiversity conferences. Although both teachers had encouraged making a grid of the yard to guide their observations, the students initially did not see the need to map or develop a systematic plan. The students had begun with an “Energizer bunny” strategy: look around, write down novel species, and keep doing that until you don’t see any more. In comparing results between the two classes—and hence comparing the east and west sides of the schoolyard—the students realized that they needed to be more systematic in figuring out the distribution or density of common species. In order to do this, they shared mapping techniques and some strategies for sampling to characterize the woodlot and ravine areas (using compasses and pacing) and made explicit decisions about where, how, and what to sample (see Figure 2-2).

With more accurate maps, they began to speculate about the causes of variation in plant and animal life. They wondered if a species often grew in one place rather than another because of the other things growing around it. Careful observations that included shade, position on a slope, and distance from a path where the soil is disturbed took on new significance. They noticed that there were more trees and larger trees on one side of the schoolyard than there were on the other, which prompted a great deal of theorizing about the cause: Was it sunlight, soil quality, or amount of water? This, in turn, led to more systematic measurements of tree circumference and height. Mr. Walker and Ms. Rivera realized that the students’ decision to use systematic measurement had to be motivated by their own theories and investigations in order to be seen as a necessary and useful technique.

After several months, a number of the students in each class emerged as highly skilled draftsmen

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