The diversity of life on Earth is a fundamental concept in biology, but it can be difficult to explore in the confines of an elementary school classroom. A great place to start is by getting students outside to observe the diversity in their own backyards. The author served as a scientist-in-residence for one year at an elementary school in Missoula, Montana, working on ecological inquiries inside and outside of the classroom. To extend students' learning beyond their local area, she set up an ecological pen pal exchange with students at two schools in northern Scotland. In their exchange, they focused on the broad differences in biodiversity between their two countries. This approach introduced younger students to the concept of biodiversity: They learned about why different species inhabit different places, and compared the species found in Scotland and Montana. They also explored how the environment affects living organisms by making observations of birds in their school yards over multiple seasons. In this article, the author describes how they developed this project and shares some of the tangible results of the exchange, with suggestions along the way for how to implement this kind of project in the classroom. (Contains 3 figures.)