Decades of research have established effective curricula for struggling readers. In the digital age, educational technologies expand access to apps and resources to supplement classroom instruction, but most lack scientific backing. "Sound it Out," a collaborative effort between reading researchers and technology developers, aims to address this disconnect. This dissertation describes the design and development of the "Sound it Out" tool using three intervention studies of children ages 7-15 (n = 175). Each study answers questions of efficacy and the context for which this tool is ideally suited. We find that, with practice, emerging readers can effectively leverage the tool's symbolic vowel annotation to decode novel words more accurately. We also find generalizable gains with extended practice and enhanced benefits with caregiver-supervised usage. Results demonstrate that "Sound it Out" is an effective scaffold for vowel recognition in emerging readers. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]