One of the most important educational challenges in developing environmental literacy for sustainability is understanding systems thinking. For example, grasping the effects of humanity’s disruption of the natural carbon cycle is crucial for making informed choices about climate change. Although development of systems thinking skills is challenging, they could be promoted through interactive visual learning environments. In the present study, we explore pupils’ use and assessment of a newly developed interactive learning environment, termed “Tracing Carbon”, designed to support grade 7-9 pupils’ systems thinking skills in the context of the carbon cycle. Data were collected from two classes (n=63) that engaged with Tracing Carbon as part of their science class. Performance was assessed by analysing log files of interactive tasks. Further information was gathered from the number of errors and perceived difficulty in pupils’ responses to quizzes in the system. The results indicate that the errors made when performing tasks can be related to misunderstandings such as believing that trees obtain their nutrition from the soil rather than from carbon dioxide in the air. Moreover, the quiz items that were designated “easy” were associated with fewer mistakes and a lower perceived difficulty rating than quiz items designated as “hard”. Future qualitative analysis could reveal links between the hierarchy levels, the number and type of errors in both tasks and quizzes, and aspects of the communicated carbon cycle content.