This study investigates how ninth-grade students in Swedish compulsory school describe and explain a technological system: the wastewater system. The analysis focuses on students’ verbal explanations while illustrating their self-drawn models of the system. Eleven students (aged 15–16) participated through semi-structured individual interviews. Transcripts and models were analysed using Hallström et al.’s (2022) classification model for system understanding and thematic analysis. The results indicate that most students were able to identify the system’s purpose, namely, the collection and treatment of domestic wastewater, and describe components such as household outlets, sewer pipes, and treatment plants. However, their descriptions were largely linear and focused on visible components, such as inlets and manholes. Few references were made to energy flows, information control, system boundary, or interdependencies with other systems. Most students’ reasoning remained at the Multistructural level; only two demonstrated relational understanding, and none reached an extended abstract level. The thematic analysis revealed that students faced difficulties in understanding temporal processes, feedback mechanisms, and the consequences of system failures, highlighting difficulties in grasping system complexity. The study calls for instruction that explicitly makes hidden structures, interconnections, and sustainability aspects visible in technological systems. It proposes combining student-generated drawings with visualizations, simulations, and structured reflection to promote deeper and more transferable systems thinking in technology education. Although grounded in a Swedish context, the findings and suggested teaching strategies may inform broader educational settings and contribute to strengthening systems thinking as a core competence in technology education globally.

Background: Understanding technological systems is essential for students to participate in and critically engage with a technology-rich society. Prior research indicates that pupils often find it challenging to grasp the structure, function and dynamics of such systems. Purpose: This study investigates how Year 6 pupils (aged 10–12) describe, explain and analyse a technological system–specifically the wastewater system–and what their self-drawn models reveal about their systems thinking. The aim is to contribute knowledge on how pupils conceptualise complex systems and how this can be pedagogically supported. Sample: Seven pupils from different schools in Sweden participated in individual interviews. All had received instruction about the wastewater system, including a study visit to a treatment plant. Design and methods: Data was collected through semi-structured interviews. Pupils were asked to explain the wastewater system and draw a model of it on paper. Thematic analysis was conducted inductively to identify patterns in the pupils’ verbal and visual descriptions. In the discussion, the Freiburg model of systems thinking was used as a conceptual framework to interpret the findings. Results: Pupils often began their reasoning from system-related problems, such as blockages. Most described the system as consisting of subsystems and components, although some expressed a more linear or circular view. Their self-drawn models supported verbal explanations but also revealed misconceptions about flow mechanisms–especially the role of gravity, which was often overlooked or replaced by flushing or pumps. Conclusion: The study shows that pupils’ drawings help structure their reasoning and support systems thinking. However, simplifications in the models may lead to misunderstandings. Teachers should guide pupils through technological systems ‘from source to end’, clarify key concepts and scaffold the model-building process to enhance accuracy and holistic understanding.