A classroom discussion started after a student noticed three days of accumulated trash in the wastebasket and exclaimed, "Wow, look at the trash! If it keeps piling up like this, it will soon be everywhere!" His statement motivated the authors' class to research about the trash, or solid waste, we create and what can we do about it. The project-based learning (PBL) unit shared in this article allows students to learn about solid waste management, actively construct their ideas, and collaboratively engage in tasks that emphasize the connection of science and mathematical knowledge. The unit, taught to fifth- and sixth grade students, engages students in science concepts such as solid waste, recyclables and nonrecyclables, and the students' neighborhood area. It was spread over a period of six weeks, and two hours every week were spent discussing and researching the driving question: How does the solid waste I create affect my community? In this article, as researchers and teacher educators who crafted this unit, the authors reflect on what was done each week in the classroom with students.