PROJECT SUMMARY Absent known deficits such as hearing loss or developmental disorder, approximately 15% of two-year-olds nevertheless have atypically small expressive vocabularies. These “late talkers” (LTs) are at increased risk for a later diagnosis of language disorder, and even those LTs who are not diagnosed still have poorer long-term language outcomes as compared to their typically developing peers (TDs). At present, we do not know why some children struggle to develop their vocabularies, and we are unable to predict which LTs are at greatest risk for language disorder. This project focuses on toddlers’ verb vocabularies because of the role that verbs play in developing grammar. Difficulty with verbs is considered a warning sign for later language disorder, and children with language disorder in turn struggle particularly with verbs. To learn new verbs, toddlers use information derived from the surrounding linguistic context, such as sentence structure. However, this ability is predicated on preexisting knowledge of verbs. Concerningly, our prior research indicates that LTs and TDs differ in early verb knowledge: LTs have more result verbs (i.e., verbs that denote the result of an event, such as “break”) than manner verbs (i.e., verbs that denote how an event unfolds, such as “run”) in their vocabularies. This pattern mimics biases for result over manner meanings observed in older children with language disorder. However, TDs have more manner than result verbs throughout development. In contexts where verb learning is dependent on knowledge of manner versus result meanings, LTs and TDs are likely to perform differently. In Aim 1/Study 1, we consider one such manipulation: Whether the sequencing of the linguistic information (i.e., the verb) and its referent action impacts verb learning. TDs appear to learn manner verbs best when the verb precedes the action, but they learn result verbs best when the verb follows the action. However, older children with language disorder better learn verbs when they follow the action, irrespective of verb meaning. We hypothesize that LTs will show the same pattern as older children with language disorder because they also have a bias for result over manner verbs. If true, this would be the first demonstrated verb learning difference between LTs and TDs. Learning a verb’s meaning from its linguistic context also requires that children be able to process the given linguistic information. Conversely, children who do not process the linguistic context fail to learn new verb meanings. It has been hypothesized that children who are faster linguistic processors are better verb learners, but this has not yet been demonstrated experimentally. In Aim 2/Study 2, we consider the relationship between concurrent processing of familiar words and performance on a verb-learning task (i.e., Study 1). We hypothesize that for both LTs and TDs, those who are faster to process familiar words will also be better at verb learn...