We argue that the distinguishing features of Participatory Design
are not the participatory activities as such but the mechanisms used,
the effects produced and the way in which these are sustained. We
use program theory to illuminate how participatory design works
and how it may be understood as more than a collection of methods or a matter of configuring user participation. Program theory
operates by formulating the causal relations between the planned
inputs, the process and the effects in terms of output, outcome
and impact. While participatory design might appear similar to
co-design or user-centered design on the level of design activities,
PD differs in terms of the mechanisms employed and how effects
and their sustainment are conceived. Looking at participatory design through the lens of program theory highlights how particular
mechanisms work towards not only the designed product but also
towards generating gains and lasting effects for participants.