Second language acquisition research often compares non-native acquirers (L2ers) with other learner populations. Such cross-population comparisons include: (i) child native language (L1) acquisition~child L2 acquisition (e.g. Gavruseva 2000; Weerman et al. 2003); (ii) child L2~adult L2 (e.g. Cancino et al. 1978; McDonald 2000; Montrul 2002; Weerman et al. 2003) and (iii) child L1~adult L2 (Canc...