This paper was aimed at clarifying the significance of instructional methodologies used by senior-phase teachers to integrate environmental education. The researcher’s empirical evidence evoked interest in this paper; the researcher noted that senior-phase teachers would barely integrate environmental education and if they did, they would only rely on an outdoor teaching method. This observation piqued the paper's attention. A qualitative interpretive multiple case study method was used. This paper was conducted in three senior phase schools in the Nkangala district in the Mpumalanga province of South Africa. Three teachers who taught natural science, technology, and life orientation subjects were sampled purposefully. Data were obtained through semi-structured interviews and pre- and post-lesson observations, and a typology approach was used to analyze data. The main research findings were that these teachers had confusion about which instructional methodologies to use when integrating environmental education. Furthermore, this paper revealed that the use of instructional methodologies such as narrative, lecture, project, jigsaw, textbook, and student team accomplishment division methods hampered environmental education integration inadequately. Nonetheless, instructional methodologies such as the interactive method, the outdoor learning method, the question-and-answer method, and the discussion method allowed some of these teachers to integrate environmental education effectively. Therefore, to ensure that there is an education for sustainable development and that teaching and learning are responsive to the Sustainable Development Goals. It is recommended that the curriculum implementers and teachers establish ongoing environmental education programs consistent with South Africa’s Curriculum Assessment Policy Statement to enable adequate integration of environmental education through various instructional methodologies.