This column focuses on promoting learning through assessment. In 1999, a group of researchers from Indiana University and Purdue University decided to investigate data about students' ideas in science by inviting National Science Teachers Association members to participate in a research study about children's conceptions of animals. Published in "Science and Children" (Barman et al. 1999), the article received an overwhelming response from K-8 teachers across the nation interested in participating in this national study by collecting and submitting their own student data about students' perceptions of animals. A year later, results of that study were published in "Science and Children" (Barman et al. 2000). The "Is It an Animal?" justified list probe is similar to the set of examples used in Barman's (1999) study. It includes a variety of animals as well as a few nonanimal examples. In the probe, students are encouraged to describe the "rule" or reasoning they used to decide whether something on the list is an animal. This probe is particularly useful to the elementary teacher as the concept of "animal" appears frequently in the elementary curriculum, children's stories and trade books, and popular television programs. This column discusses having teachers conduct their own study regarding students' thoughts on whether something is or is not an animal. (Contains 1 figure.)