This thesis seeks to explain social participation in pre-schools for children with and without Down’s syndrome. The explanation is achieved by use of an explanatory model of social participation, designed on the basis of critical realism, which has been used in an empirical study of how social participation emerges in practice. Mechanisms have been abstracted. It is assumed that recognition mechanism produces social participation and reification mechanism social exclusion. The results show that the agency of the personnel affects the possibilities for the recognition mechanism to produce social participation. Within the agency of the personnel, the internal relationship between the child perspective, i.e. how children's place in society is understood, and the relationship to the child's perspective, i.e. how children's participation is regarded, either prevents or makes possible activation of the mechanism. The child perspective has, through the empirical study, been seen to take two different forms: either that children are similar, with similar needs, or that they are different, with different needs. If children are defined as similar, the structures will accommodate all children, enabling them to be socially involved in the same activities. If children are defined as different, different structures are created for different groups of children. Groups are segregated from each other, preventing the children from being socially involved in joint activities. The relationship to the child's perspective has emerged in relation to the roles of the child as an agent, as a collective subject, and as an individual subject. The role definition affects the degree of constraint imposed on the possibilities for action that are offered, and thus affects the opportunity costs and degrees of freedom of the children. These determine the activation of recognition mechanism and social participation in the situation.