Private supplementary tutoring (PST) is a phenomenon growing throughout the world. Looking at regions such as East Asia where it is already vast and comparing with regions where it remains modest but is rising, some authors have argued that countries must act quickly to discourage negative societal implications which arise when PST grows. One underpinning suggestion here is the notion that addressing PST may be "time-critical." Drawing on insights from political science on the nature of continuity and change, in this paper I explore the possibility that societies could become substantially 'locked in' to complex patterns of dependence on PST. I report on the case of South Korea, drawing on interviews with experts in the Korean education system. I show that parents have been incentivised progressively over time to layer 'shadow education' over public schooling, particularly in times of heightened anxiety. Governments meanwhile have faced disincentives to restrict PST and public school teachers have had to adjust to becoming perceived as offering a residual service.