This article reports a subset of findings from a larger study centered on designing a series of six digital learning objects to help Grade 5 (age 10-12) students begin to consider the nature of models (understood as the physical or mental representation of objects, phenomena, or processes), the particle nature of matter, and the behavior of particles during physical and chemical change. Results show that students were able to identify key differences among particle models and write about how particle movement and spacing could be used to explain the observable properties of matter. Students endorsed the idea that models were not exactly like the real thing. Within the context of particle models, however, it was difficult for them to write about how these models did differ from the real thing. Instead, they reasoned that the models were used to show what particles might look like or to see particles up close. Curriculum developers are advised to reconsider what could be gained by introducing Grade 5 students to the particle nature of matter after exploring the observable properties of matter. (Contains 7 tables and 4 figures.)