This study contributes to the emerging literature on the diffusion of SPC across social strata, by comparing two national contexts, Sweden and Spain, with different prevalence rates of SPC and with diverging social and gender policies in the early XXI century. We draw on the 2006 and 2014 comparative cross-sectional data from the Spanish and Swedish Health Behaviour in School-Aged Children (HBSC), to test two competitive hypotheses (diffusion and diverging destinies hypotheses) on the association of parental socioeconomic status, children’s living arrangements in separated families and their relative prevalence in a populaiton. We also examine whether such association is modified by the great increase in SPC in both countries between 2006 and 2014. We present empirical evidence that, independently from the context, SPC arrangements are more frequent among parents with higher socioeconomic status and sole-custody arrangements among other parents; however, social inequality in post-separation arrangements differ in the two countries over time. In Spain, we find evidence in favour of the diffusion hypothesis with increases in the prevalence of SPC going hand in hand with the diffusion of SPC across social strata. By contrast, the Swedish data support the diverging destinies hypothesis with increases in SPC producing no variation in its social stratification over time.