This study investigates conditions and factors that affect preservice teachers' decisions to use handheld computers in scientific investigations and explores aspects of student learning and classroom practices that would be affected by handheld-based science activities. A Handheld-Based Laboratory (HBL) was designed to model strategies for integration of mobile technology into Science Methods courses and to create a conceptual change in preservice teachers' attitudes towards technology. Participants included 21 preservice teachers in a Science Methods course. Five conditions that can affect the integration of handheld technology for instruction and learning emerged from this study: (a) classroom and school environment, (b) teachers' technological background and predisposition, (c) students' prior knowledge and experience, (d) open and engaging curriculum, and (e) access to handheld computers as learning tools. Use of handheld-based science activities also enhanced preservice teachers' inquiry abilities, organizational skills, engagement in science content learning, and attitudes and self-efficacy.