Language aptitude comprises cognitive and perceptual abilities that predispose individuals to learn well or rapidly (Carroll 1981; Doughty et al. 2007) and that can interplay with age by moderating its effects on learning outcomes. Although there is agreement regarding the importance of aptitude, findings have been mixed regarding its role in child second language acquisition (e.g. Abrahamsson and Hyltenstam 2008 vs. DeKeyser 2000). This study set out to investigate whether aptitude played a role in ultimate morphosyntactic attainment by a group of early childhood learners. Participants completed a speeded-response and a non-speeded-response grammaticality judgement test (GJT), and the LLAMA aptitude test (Meara 2005). Results showed the presence of an interaction between aptitude, test, and target structure. Aptitude was significantly related to early learners' attainment in structures involving grammatical agreement on the non-speeded-response GJT. This was interpreted as showing the compensatory role of aptitude in structures for which age effects are the strongest and a relationship between measures of aptitude weighted in favour of explicit cognitive processes and untimed measures that induce learners to approach language analytically.