Project Summary: Children with language disorders are at risk for a host of negative health and academic consequences, and represent at least 7% of the school-aged population. This project addresses two critical public-health needs regarding language disorders: (1) Characterizing early lexico-semantic skill trajectories with the goal of (2) Improving early identification. We focus on several promising assessments of lexico-semantic abilities in toddlers, as lexico-semantic skills are a component of language which is affected in school-age children with developmental language disorders, and can also be reliably measured in toddlers. We propose to recruit a large group of 18-month-old toddlers with a diverse set of language abilities and backgrounds and then follow these children longitudinally to assess whether and how growth in three main lexico-semantic skills (structure, learning, and processing) predicts language outcomes at age 4, when clinical language disorder status can initially be assessed. To fully characterize how early skills and trajectories lead to later outcomes, we carry out several analyses on concurrent and predictive relations between skills and create detailed models of children's early lexicons. This project will advance our ability to detect early language disorders by evaluating the degree to which early skills in recognizing relationships between known and novel word meanings might serve as a marker of longer-term language delays.