Saving the World–One Ecosystem at a Time is Activity 8 from the NSTA Press book “Doing Good Science in Middle School.” In this activity, teams of students research and design a solution to maintain the health of their chosen ecosystem. The driving question, “What goes on in an ecosystem that makes it function?”, helps support students’ thinking about solutions to maintain the health of their chosen ecosystem. Teams will evaluate the merits and the constraints of each of the possible solutions from their research, rank those solutions, and present oral arguments defending their top solutions. By the end of this activity, students will have demonstrated the ability to research and then present an evidence-based argument proposing various solutions to maintain biodiversity and equilibrium in an ecosystem. The resource suggests that a hands-on approach could include micro-systems such as a jar covered with plastic, bacteria in a petri dish, a terrarium, or local ecosystems. The teacher should be aware that these micro-systems are limiting for the Performance Expectation but could be used secondarily to a full-scale ecosystem.