Connections among the mathematics, science, and engineering disciplines have been recognized and affirmed in national standards. For example, the application of mathematical ideas and skills within science has been highlighted in national science standards for over 20 years. More recently, the Next Generation Science Standards (NGSS; NGSS Lead States, 2013) incorporated computational thinking (Wing, 2006), engineering design, and a K-12 strand of performance expectations in engineering, technology, and applications of science. To ensure opportunities for mathematical development within a science context, a focus on mathematical modeling can be productive (Stohlman, 2018): a process of using mathematics to represent, analyze, and make predictions regarding complex, reality-based phenomena (Garfunkel & Montgomery, 2019). The importance of developing students' capacities for mathematical modeling at every grade level is underrealized, yet it offers noteworthy advantages for deep mathematical learning while also charting a way forward in mathematics and science integration. This article examines how an elementary teacher integrated mathematics and science to engage fourth graders in an authentic inquiry exploring sustainability solutions for their school.