Children's ability to self-regulate varies across days and contextual demands. However, the predominant approach in developmental science is to assess self-regulation at a single timepoint in one context, limiting our understanding of how and why children's self-regulation skills vary intra- and inter-individually. The present study addresses this gap by repeatedly observing children's self-regulation in the classroom 10 times during two different classroom activities. The sample consisted of N = 201 Swiss kindergarteners (47.8% female, M = 5.4y., SD = 0.6). We assessed children's self-regulation using an observational measure that captures two self-regulation dimensions: attention control and inhibitory control. To analyze self-regulation variability, we used multilevel location-scale models in a dynamic structural equation modeling framework. The findings indicated substantial intra-individual variability in self-regulation across the 10 classroom observations. Moreover, children differed significantly in the degree of intra-individual variability. When controlling for class membership, differences in attention control variability were related to the teacher-student relationship closeness. Differences in inhibitory control variability were associated with children's gender, with boys showing higher variability than girls. Overall, the present findings indicate that young children's self-regulation skills can vary substantially across days and classroom activities. These findings emphasize the importance of considering the role of momentary regulatory demands in children's self-regulation capacities.