Too often, mathematics and science are taught in isolation from each other and from meaningful problems that matter to students. This book draws on the authors' experiences with teacher colleagues, including time spent in their classrooms co-developing and refining lessons. The core of their approach is to encourage learners to pursue solutions to everyday challenges through design-based learning cycles. Students use mathematical modeling to describe or summarize a phenomenon, predict which potential solutions may be successful, and/or to test actual performance against predictions. The authors emphasize connecting grade-appropriate science and math content standards and integrating literacy with evidence-based argument through design briefs and presentations. Teachers will learn how to support productive struggle and structure group learning that promotes equity, while teaching in the classroom or virtually as needed. The middle grades are a pivotal time to engage the next generation so that they are prepared to solve tomorrow's challenges. Classroom teachers, pre-service educators, and faculty in teacher education programs can use Design Thinking in the Middle Grades as a foundational text for math, science, and integrated STEM teaching.