This study discusses some of the paradoxes found in the rhetoric of participatory research. Research-with-children views them as competent and agentic and as social actors, as citizens with opinions that must be listened to and given due weight. This image of the child as a social actor fails to acknowledge the structural, contextual and relational conditions that can afford or restrict opportunities for children's agentic action. It conceals the multi-faceted, multi-dimensional properties of power that shape children's (and adults') contributions and 'voices'. Our research took place in a primary school and aimed at training Year 6 children to carry out their own research on their chosen topic of interest. The participatory research 'space' was informed by the participants' different intentionalities and agendas. The children were invited to take initiatives and make decisions, to be agentic. However, their agency, or what counts as 'proper' agency, was framed and defined in our adult terms. Tensions arose when the children's agendas conflicted with and threatened ours. As we argue here, this participatory space should rather be seen as a political arena, where different and often competing agendas are at play, where the roles and relationships between children and adults are far from fixed, and where the capacity for agentic action is always socially mediated and shaped by social structure.