In order to facilitate the comprehension of social structure in preschool children, our research has two foci: first, to define controlling behaviours (nonaggressive group organisation) and to determine their organisational principles, and second, to analyse the relation of the controlling behaviours with aggressive behaviours. Through direct observation, the behaviour of 90 preschoolers aged 4-5 years old during free playtime was registered. A correspondence analysis revealed that two organisational principles structure controlling relationships, one related to authority and another to acquiescence. The independence of these two dimensions suggests the existence of a social hierarchy in preschoolers' playgroups based on controlling behaviour. No significant relation between authoritative and aggressive behaviours in 4-year-old children was detected, while 5-year-old children with high levels of authoritative behaviour were less aggressive than individuals with low levels. Our results point out that controlling activity is relevant in the organisation of preschool children's social groups. Children's goal development probably determines the change of the behavioural strategies that facilitate the evolution of social structure from aggressive to controlling hierarchies. We judge it necessary for research to focus on controlling interactions. (Contains 2 tables and 1 figure.)