Acquiring key competences is a priority in contemporary education. According to some authors, eco-trails provide an opportunity for training in natural ecosystems. The purpose of this study is to examine the capabilities of a constructivist design for learning that is close to nature with respect to acquiring practical knowledge, motivation, and formation of environmental competencies in students. To verify this assumption, the following methods were applied: curricula analyses of teaching biology in secondary schools (Grades 5–8, Ministry of Education and Science of Bulgaria) and high schools (Grades 9–10, Ministry of Education and Science of Bulgaria), and pedagogical experiments and surveys among students for approbation of a model for environmental education that is close to nature. A syllabus for selectable (optional) training on ecological topics was developed. A model of ecological training, “close to nature”, was devised through the constructivist design and active approach, and in approbation of the model, students acquired practical knowledge, formed environmental competencies, and an increase in their motivation to protect the ecological balance.