One definition of design is "creating something new that fits with reality" (Stults, 1985). This article describes a project in which the researchers started with the intuition that new handheld-based wireless technologies held the promise of creating something new and highly desirable for K-12 education. We saw the potential for handheld-based activities to enable deeply needed formative assessment, that is, teachers' and students' own monitoring of learning for the purpose of improving teaching and learning. From prior research and our own experience, we knew of several barriers to the adoption and success of new technologies in K-12 classrooms and (separately) new science inquiry methods. Taking these barriers seriously led us to ethnographically-based activities oriented toward understanding "the reality" to which our designs needed to fit. Initial efforts to understand the variety of attitudes, experiences, and conditions in one school district caused us to make hard decisions about our priorities. In this article, we describe the realities we found and the implications we drew from them for our project, which we argue have broad import for the design of handheld technologies for schools.