This paper brings together two areas of considerable interest to researchers, practitioners and policy makers: young children's developing self-regulation and metacognition, and the impact of adult (practitioner) presence or absence on their behaviour and learning. One hundred and twenty-eight observations of 29 children aged 4-5 years in a reception class were analysed using a behavioural coding scheme. While the data show that adult presence and absence were both supportive, children were often significantly more likely to show evidence of self-regulation and metacognition when adults were absent. When present, adults were a focus for the children's attention, and children appeared to cede some responsibility to them, more frequently looking to adults to set goals, allocate roles, check and correct progress and resolve disputes. At the same time, adults played a crucial role in supporting children's procedural knowledge when they were present. Children were keen to display their knowledge to these significant people and often chose to direct their comments to adults. It is suggested that the question of how adults can supportively become involved in young children's activity deserves closer attention, particularly in the context of the development and display of young children's self-regulation and metacognition.