We all live in fragmented ecosystems where the diversity of trees, shrubs and herbaceous plants, mosses, ferns, lichens, fungi, bacteria, vertebrates, and invertebrates deserve our highest appreciation. All of these organisms are essential to maintaining a healthy and livable environment, as each of them has its place and function in ecosystems. This chapter focuses on the role that school gardens can play in conserving biodiversity by providing a variety of habitats and raising students’ awareness of various biodiversity-related aspects of sustainable development. First, the structure and functions of an ecosystem are explained from a scientific perspective. Then, different types of mini-ecosystems in the school garden are presented, and suggestions are given for creating biodiversity sites, learning spaces, and places of well-being.