In one example, a teacher working on an evolution unit conducted a series of lessons aimed at the question: Are humans similar or dissimilar to other primates? Early in this unit, she put up poster paper and drew 4 “buckets” of evidence. One bucket dealt with the amino acid structure in tissues of humans and other primates. Another bucket was for skeletal morphology, another was for brain structure, and another for behavior (mating, territoriality, troop cohesion, etc.).
As students engaged in various readings and activities, they, together with the teacher, began to place evidence for or against the similarity hypothesis into the buckets. Near the end of the unit, the students were asked to look across the various types of evidence and make comparative judgments about the strength of the similarity hypotheses. In creating names for the bucket categories, a teacher should consider what the source of the evidence is or consider how the evidence could be used to make judgments about the hypothesis, explanation, or model. It is helpful if more that one type of evidence can go into a bucket category.
This categorization into bucket categories is a lot like what scientists do and how they talk about “types of evidence.” Its prompts kids to refer to evidence they have discovered by the way it can be used (such as “genetic evidence”), rather than referring to it by the arbitrary name of the lab exercise that generated it (i.e. “the opposable thumb lab”).
As with the other public records in which students are talking about evidence and explanation, they need to know what it is they are trying to explain, so the use of evidence buckets is often combined with the early development of an initial consensus model (see #1 of public representations of student thinking).
Watch Melissa talk about how Brian used evidence buckets in his high school unit on the physics of sound.