among physical, chemical, and biological factors.

In the process of data analysis, student teams review their findings, look at ranges of data and trends over the period of study (it is spring), and determine what is appropriate to consider and how to deal with anomalous data. During their group work, Ms. Idoni moves from group to group and asks questions, such as “What explanation did you expect to develop from the data?” “Where there any surprises in the data?” “How confident do you feel about the accuracy of the data?”

After two months, the groups present their data and their explanation of the specific effect the factors they studied have on the lake and if the effect would count as pollution. As students listen to the different groups, they recognize and analyze alternative explanations and models for understanding stability, change, and the potential of pollution in the city lake. They review what they know, weigh the evidence for different explanations, and examine the logic of the different group presentations. They challenge each others’ findings, elaborating on their own knowledge as they help each other learn more about their particular factors. Slowly, they form the view that all factors have to be considered in any explanation for pollution of the lake.

To Ms. Idoni’s surprise and pleasure, the students decide that they want to synthesize the data and formulate an answer to their guiding question. Their observations and explanations continually expand; they find they have to consider factors they did not originally think were important, such as season, rainfall, and the activities of domestic animals.

As they compile all of the evidence and begin the difficult task of answering their question, they realize they must first address the question: “What counts as pollution?” The students decide that they will use coliform bacteria because of what they learn in their reading. The literature points out that water can look, taste, and smell perfectly clean and yet be unsafe to drink because it contains bacteria. This eventually becomes the students’ operational definition of pollution. They learn that coliform bacteria live longer and are easier to detect in water than bacteria that cause disease. Their presence is considered a real warning signal of sewage pollution. If coliform bacteria are not present in city lake, then, the students reason, the answer to their question is that the lake is free of pollution — at least by their operational definition of human pollution.

Working across groups, the class compiles their respective reports and prepares one major summary of their inquiry. They also include summaries of their respective results. The reports are excellent. Students capably describe procedures, express scientific concepts, review informa-

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