In the literature, marginalisation is vaguely defined as a state, a process, or both. Qualitative research has indicated that many students experience temporary marginalisation at some point in school, suggesting that the phenomenon is best characterised as fleeting. This presents a challenge for researchers in terms of measuring marginalisation as a (more) fixed state, making it difficult to assess the scope of the problem. Data on students (grades 4-10; ages 10-16) from Programme for Learning Management (N = 122,756) were analysed across three measurement points (2015, 2017, and 2019). The Social Marginalisation Scale (SMS) was developed to specifically measure the social aspects of marginalisation on a scale [1-5]. It was subsequently divided into four equal intervals. It was estimated that 3-3.5% of the students experienced social marginalisation to a high or very high extent. The degree of social marginalisation was largely stable across measurement points, indicating that some students experience prolonged social marginalisation. Grade level and gender were both significant predictors, indicating that girls and younger students experience greater social marginalisation on average. A longitudinal study is recommended to identify student groups who experience prolonged social marginalisation.