Teachers increasingly use virtual manipulatives and other apps on touch-screen devices (e.g., "iPads") in an effort to help students understand mathematics concepts. However, students experience these apps and their affordances in different ways. The purpose of this article is to inform teachers' decisions about app implementation in the classroom through discussion of four case studies illustrating ways children interacted with the app "Motion Math: Zoom," and how these interactions revealed, concealed, and developed children's mathematical understanding. These results suggest that mathematics virtual manipulative apps on touch-screen devices can be useful tools when thoughtfully implemented. Teachers can balance technological distance by assisting students who need help as they learn the technology required to interact with the app. This may include explicitly using scaffolding provided by the app, leading a guided introduction, or reminding students about appropriate interactions after an initial exploration phase (e.g., Aronin & Floyd, 2013). Both the interactions with apps (e.g., Tucker, 2015) and the discourse involved in these experiences (e.g., Anderson-Pence, 2014) can serve as formative assessments, revealing development of mathematical understanding.