Background: Self-regulation is crucial for children's learning and development. Several studies have explored children's inter-individual differences in self-regulation, but little is known about sources of intra-individual variation. Aims: This study addressed the variability of children's self-regulation across typical classroom situations and how this might be associated with children's executive functions (EFs). Sample: The study included 148 children (54.7% girls; M[subscript age] = 56.73 months). Methods: Self-regulation was assessed with an observational measure in teacher-led and child-led activities within naturalistic classroom settings. Children's EFs were assessed with direct assessments at the start and end of the school year. Results: Linear mixed-effect models showed that children demonstrated higher levels of self-regulation in child-led in comparison with teacher-led activities. Children with higher levels of EFs at the start of the school year showed less variation across teacher-led and child-led activities in comparison with children with lower levels of EFs. Regarding other aspects of the classroom context, neither the group size in which the activity took place nor which school subject it was focused on were associated with children's self-regulation. However, in teacher-led activities the type of interaction involved in the activity and the type of task influenced children's self-regulation. Conclusion: These results suggest that children who start school with higher levels of EFs are more able to adapt to different situations, highlighting the importance of fostering these skills in early childhood. In turn, children with lower levels of EFs may need additional support from teachers to remain self-regulated across different contexts.