In this study, we propose to analyse students' drawings using the Semiotic Cultural Psychological Theory (SCPT), a socio-cultural psychological model that integrates semiotics with dynamic systems theory. According to the SCPT framework, students-generated drawings can be analysed in terms of generalised meanings, i.e., implicit assumptions about the represented content. We applied SCPT to identify a set of generalised meanings about seasonal changes and to investigate whether they depend on students' grade level. We used a draw-and-explain task to collect drawings and written explanations about seasonal changes produced by 495 Italian 8th grade (N = 196) and 9th grade (N = 299) students. The analysis was based on Multiple Correspondence Analysis and Cluster Analysis. Five generalised meanings about seasonal changes were identified: (1) Climate; (2) Static Earth -- Sun; (3) Moving Earth -- Sun; (4) Rays -- Earth; and (5) Moving Earth--Orbit-- Sun. The emerging generalised meanings were significantly associated with students' written explanations and grade level. Moreover, generalised meanings were informed by the cultural conventions adopted in textbook representations about seasonal changes. Findings suggest that the SCPT framework can be productively used to analyse students-generated drawings about natural phenomena and to detect specific features of textbook representations that can impair the development of appropriate scientific knowledge.