to the fifth-grade science class he would be teaching that year. Because a major part of his college course on biodiversity had been preparing a local field guide based on weekend trips to a field station, he and a colleague, second-grade teacher Alicia Rivera, decided to work together to develop a yearlong project mapping the plants and animals in their schoolyard. To compensate for the lack of existing science materials, he and Ms. Rivera decided to combine fieldwork with some simple technology involving a computer and a scanner that Mr. Walker brought from home, as well as the school’s website. They imagined that in the beginning the simple task of cataloging the species in their schoolyard would occupy much of the students’ time. Once fewer new species were found, students could begin to focus on observing the behavior of different species and changes in the density and distribution of populations.

From the college course Mr. Walker had taken, he knew that selecting biodiversity as a theme afforded the opportunity to develop central biological principles important to evolutionary thinking, such as:

• Organisms can be described as collections of attributes and can be distinguished (classified) by variation among these attributes.

• Change in selected attributes of organisms (e.g., plant height) can be modeled mathematically, so that comparative study of patterns of change can be conducted at the organismic level, a level with great initial appeal to students who grow their own plant or care for their own insect.

• The “natural histories” of organisms (e.g., life cycles) could be described and compared.

• Growth can be aggregated at several levels (genotypic, phenotypic, population).

• Population growth can also be modeled mathematically. Heritability and selection transform distributions of selected attributes in populations, giving concrete meaning to differences in levels of analysis.

Moreover, in preparation, Mr. Walker and Ms. Rivera spent time discussing the science behind their schoolyard investigation. They sought out field guides and other text resources which helped them see that understanding behavior is central to both the social and the biological sciences and entails grasping a set of interrelated concepts, including:

• Descriptions of behavior vary in their level of detail (e.g., micro to macro) and in their scope of application (e.g., behaviors of individuals, groups, populations, and species).

• All organisms have repertoires of behavior that are species specific. One can often identify reliable patterns in behaviors. Some behaviors are automatic and relatively inflexible; others are under voluntary control and are relatively flexible.

• The form and/or functions of behaviors may change over the development of an organism. Sometimes a behavior maintains its form while its function changes; other times, organisms develop new behaviors to achieve a similar function.

Mr. Walker and Ms. Rivera spent time discussing the mathematical resources useful in modeling behavior, including representations of frequency, covariation, distribution, function, and classification models. Mr. Walker brought in notes from his college class about domain-specific models of behavior that could be developed with students, including rules, programs, ethograms, and information-processing models.

Ms. Rivera and Mr. Walker also had a large number of students who spoke Spanish at home and a few students who were just learning English. Their hope was that the project would get both English-speaking and Spanish-speaking students excited about