This paper presents the results of applying the Learning by Teaching (LdL) method in vocational secondary education, focusing on learning areas such as environmental protection, sustainable construction, waste management, the use of natural materials in construction, the transition to green building technologies, recycled concrete materials, and nature-oriented design. The research was conducted with students of the Construction Technical School in Zagreb, in the fields of architectural and building technicians. The method was implemented in classes with a sample consisting of 45 vocational secondary school students and, in a previous phase, 100 primary school students.

Students were organized into teams of five members, with each team addressing a specific topic through literature research, extraction of key terms and concepts, preparation of bullet points on those concepts, formulation of questions and answers, development of a PowerPoint presentation with illustrative content, and writing a summary of the topic in English. Each group delivered a 10-minute presentation, followed by discussion and peer evaluation.

The objectives of the student activities were to motivate active and autonomous learning, develop technical vocabulary in both Croatian and English, enable critical thinking and argumentation, and strengthen teamwork, time management, and the use of diverse learning resources.

The learning outcomes included structuring the learned content through key terms, bullet points, questions, and illustrations; acquiring and correctly using technical terminology; communicating and presenting independently processed content; and conducting peer evaluation based on specific criteria.

This paper presents the Learning by Teaching method on the example of topics related to sustainable construction and green transitions. It was compared to traditional frontal teaching, in which the teacher is the primary source of knowledge and students are passive recipients of information. While frontal teaching allows for a quick transfer of basic information and provides a clear structure of content, it rarely encourages critical thinking, collaboration, and long-term retention. In contrast, Learning by Teaching places the student in an active learning role, fostering higher-order cognitive processes, teamwork, language competencies, and intrinsic motivation. However, method requires more time for preparation, mentoring guidance, and good organization of teamwork.

In the context of vocational education, particularly in topics related to sustainable development and green construction technologies, the Learning by Teaching method has proven to be a more effective approach for developing 21st-century competencies, while traditional teaching remains valuable in the initial phases of introducing teaching methods and structuring lessons, as well as when providing feedback and assessment. The best results are achieved by combining both methods, where frontal teaching serves as a guiding framework, and Learning by Teaching is used for acquiring, deepening, and applying knowledge in real-life tasks.

Keywords: Learning by Teaching, active learning, student competencies, technical vocabulary, vocational education, green technologies, sustainable construction.