Recent empirical evidence suggests that decentralization challenges the stakes of democratic control by blurring responsibility attribution between levels of government. Exploring the implications of decentralization on accountability requires a better understanding of the conditions under which decentralization affects clarity of responsibility. The theoretical claim in this article is that these conditions are related to the particular design and duration of decentralization arrangements. To test this proposition, individual data from a system where decentralization varies both in design and duration – the Spanish State of Autonomies – are used. Results show that clarity of responsibility has worsened where decentralization has adopted a more intertwined (marble-cake) design and that individuals may “learn” on responsibility attribution the longer they experience a particular distribution of competences.