Earth Day is celebrated annually on April 22. Teachers often commemorate Earth Day with their classes by planting trees, discussing important conservation topics (such as recycling or preventing pollution), and encouraging students to take care of planet Earth. To promote observance of Earth Day in an intermediate elementary school classroom, this article presents the integration of sustainability with the hopes of preserving Earth and its resources for as long as possible. This article describes a six-week unit that integrated sustainability and mathematics at the intermediate elementary school level. Students explored a topic and identified solutions that would support preserving resources for the betterment of our planet. The iSTEM (Integrating Science Technology Engineering in Mathematics) authors share ideas and activities that stimulate student interest in the integrated fields STEM in K-grade 6 classrooms.