One of the fundamental questions within developmental sociolinguistics, and language acquisition research more broadly, has to do with children’s reaction to variability in their input or primary linguistic data (e.g. Labov 1989, Yang 2002, Hudson Kam and Newport 2005, Smith et al. 2009, Cournane and Pérez-Leroux 2020). As has been extensively documented, children overgeneralize and regularize both consistent (Marcus et al. 1992) and inconsistent (Hudson Kam and Newport 2005) input. Despite this tendency to go beyond the input, we do expect children to learn their caregivers’ dialect, and they have in fact been known to match the rates of variation found in their environment (Labov 1989, Johnson and White 2019). The literature therefore shows both regularization and matching, but under different circumstances. In this paper, we argue for a third scenario and present a case where children neither regularize nor match their caregiver. Instead, they replicate the systematic contrasts they encounter and regularize within matched conditions. This is what happens in the acquisition of Icelandic Dative Substitution (DS), a stigmatized but widespread instance of grammatically conditioned morphosyntactic variation. We investigated DS in 99 children aged 3–13 and their caregivers (80 dyads) by using forced-choice tasks and grammaticality judgments across multiple items as a proxy for case use. The results show that caregivers’ general DS rate did not predict the rate at which their children selected DS, regardless of age. On the other hand, when analyzing the data within conditioning factors, we found that children replicate the contrasts present in their caregivers’ speech, both at the group and individual level, and that this was in part dependent on age
