Systems thinking is currently envisaged as a useful educational approach to teaching about sustainability (including green chemistry education) because of the high number of interrelated factors involved and the need of learners to acquire the ability to identify all of the factors and their relationships. After recalling the way in which key concepts are understood and utilized in this work, the work focuses on the challenges diagnosed in an introduction to green chemistry activity carried out within a process technology course in a disadvantaged educational context. In this process technology course, systems thinking is needed to understand the functioning of a chemical plant as a system; within the green chemistry related activity, systems thinking is needed to understand green chemistry principles, their implications for chemical production and practices, and their expected impacts. The challenges students encounter are highlighted through consideration of recurrent patterns of diagnosed inadequacies and problems. Poor language mastery is recognized as the paramount obstacle hindering the development of students' systems thinking. Ensuring adequate language mastery by the learners is an essential prerequisite to the development of satisfactory systems thinking abilities.