Stable structured layouts of buttons are a primary means of control for input in current graphical user interfaces. Such layouts are ubiquitous - from tiny iPhone screens to large kiosk screens in the malls - they are found everywhere. Yet, there has been relatively little theoretical account that compares the impact of cognitive effort on learning such stable layouts. In this paper, we demonstrate that prior empirical results on cognitive effort in learning stable layouts are theoretically predictable through the memory activation model of a cognitive architecture, ACT-R. We go beyond previous work by quantitatively comparing the level of cognitive effort in terms of a newly introduced parameter in the declarative memory model of ACT-R. We theoretically compare the cognitive effort of two different layouts of graphical buttons with respect to their label representativeness in the domains of traditional keyboard and ShapeWriter.