Many policymakers, administrators, and other K-12 stakeholders have long advocated the use of computers and information technology in schools. Even in settings where such technologies have been introduced, however, evidence suggests that the impact on student outcomes has been mixed. In some cases, teachers simply do not adopt the new technologies. A better understanding of teacher technology adoption would help both education researchers and practitioners foster technology use by teachers. In my mixed-method study, I investigated teachers' adoption of a new Web-based instructional planning system, the Curriculum Customization Service (CCS), in the context of a larger instructional challenge: how did educators adapt their instructional practices to the learning needs of a diverse student population? I found that teachers reported three major reasons for adopting the CCS: to increase their efficiency in utilizing digital resources, to offer alternative representations of key concepts, and to differentiate instruction according to student differences such as reading ability and language proficiency. The CCS also impacted both teachers' instructional planning and classroom teaching: teachers reported that the CCS helped them integrate digital resources into their teaching practices with greater confidence, frequency, and effectiveness. My study made two significant contributions to the literature on technology adoption: a new case study describing how and why teachers adopted CCS and a novel conceptual framework that characterized technology adoption according to four perspectives: quantitative, qualitative, mixed-method, and longitudinal. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]