Learning noun classification systems, like gender, involves inferring a language-particular set of (often probabilistic) cues to class membership. Previous work has shown that learners rely disproportionately on phonological cues (e.g., Karmiloff-Smith, 1981; Gagliardi & Lidz, 2014). Surprisingly, this occurs even when competing semantic cues are more reliable predictors of class. We investigate two possible explanations for this: first, that phonological cues are more salient to learners than semantic cues, and second that phonological cues are generally available earlier than semantic cues. We show that adult learners' treatment of conflicting cues to noun class in a miniature artificial language depends on both cue saliency and early availability. Importantly, learners prioritize earlier-available cues even when they are less salient than competitor cues. Our findings suggest a possible mechanism for children's over-reliance on phonology: children start building their classifications systems very early, when phonological information is available, but word meanings are not.