Teachers’ behaviour is a key factor that influences students’ motivation. Many theoretical models have tried to explain this influence, with one of the most thoroughly researched being self-determination theory (SDT). We used a Delphi method to create a classification of teacher behaviours consistent with SDT. This is useful because SDT-based interventions have been widely used to improve educational outcomes. However, these interventions contain many components. Reliably classifying and labelling those components is essential for implementation, reproducibility, and evidence synthesis. We used an international expert panel (N = 34) to develop this classification system. We started by identifying behaviours from existing literature, then refined labels, descriptions, and examples using the experts’ input. Next, these experts iteratively rated the relevance of each behaviour to SDT, the psychological need that each behaviour influenced, and its likely effect on motivation. To create a mutually exclusive and collectively exhaustive list of behaviours, experts nominated overlapping behaviours that were redundant, and suggested new ones missing from the classification. After three rounds, the expert panel agreed upon 57 teacher motivational behaviours that were consistent with SDT. For most behaviours (77%), experts reached consensus on both the most relevant psychological need and influence on motivation. Our classification system provides a comprehensive list of teacher motivational behaviours and consistent terminology in how those behaviours are labelled. Researchers and practitioners designing interventions could use these behaviours to design interventions, to reproduce interventions, to assess whether these behaviours moderate intervention effects, and could focus new research on areas where experts disagreed.