The COVID-19 pandemic has created an opportunity for K-12 schools to rethink and redesign instruction. The urgency to continue providing students with education accelerated the blend of face-to-face instruction and online learning in K-12 education. Blended learning is any formal education program that combines face-to-face instruction with online instruction. Blending learning has the potential to unlock customized learning, provide competency-based learning, and open up a world of opportunities that allows students to learn anytime and anywhere. Despite several interventions by the United States Department of Education and local education organizations, mathematics continues to be a challenging subject for students in the United States of America. To overcome the learning deficit, mathematics teachers continuously try new and innovative ways to increase student engagement while implementing and taking advantage of technology and resources available in the 21st century. For example, the promises of blended learning can be significant in helping with the challenges of middle school math, such as closing achievement gaps. Also, using appropriate technological tools in instruction positively affects students' mathematical learning outcomes. Although teachers play a critical role in achieving strategic use of technology in instruction, many teachers lack formal training in instructional design. Designing blended learning is not just using technology, but instead, it requires the use of a design process to align a model to unique circumstances. The literature indicates that aligning instructional components to ideal instructional designs benefits both the learner and instructor. However, it is unknown how teachers design or select blended learning models for unique circumstances. Ignoring the instructional design process can hinder the student learning experience and the teachers' experiences in blended learning environments. This qualitative research examined teachers' experiences and considerations in designing and selecting blended learning models. The study collected data through web interviews with middle school math teachers who have implemented blended learning models. The findings of this study contribute to instructional design processes that guide policymakers, school leaders, and teachers. These processes help match unique circumstances to appropriate blended learning models that engage students in meaningful learning experiences. [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.]