childhood and adolescence and are associated with distinct social-emotional patterns of behavior that are largely consistent with adult manifestations of those same personality traits. Some researchers have proposed the youth personality trait is best described by six trait dimensions: neuroticism, extraversion, openness to experience, agreeableness, conscientiousness, and activity. Despite some preliminary evidence for this "Little Six" model, research in this area has been delayed by a lack of available measures. Previous research has found evidence that most adults become more agreeable, conscientious, and less neurotic as they age. This has been referred to as the maturation effect. Many researchers have sought to investigate how trends in adult personality development compare to trends in youth personality development. Two main population-level indices have been important in this area of research: rank-order consistency and mean-level consistency. Rank-order consistency indicates the relative placement of individuals within a group. Mean-level consistency indicates whether groups increase or decrease on certain traits throughout the lifetime. Findings from these studies indicate that, consistent with adult personality trends, youth personality becomes increasingly more stable in terms of rank-order throughout childhood. Unlike adult personality research, which indicates that people become agreeable, conscientious, and emotionally stable with age, some findings in youth personality research have indicated that mean levels of agreeableness, conscientiousness, and openness to experience decline from late childhood to late adolescence. The disruption hypothesis, which proposes that biological, social, and psychological changes experienced during youth result in temporary dips in maturity, has been proposed to explain these findings. Extraversion/positive emotionality In Big Five studies, extraversion has been associated with surgency. Children with high Extraversion are energetic, talkative, social, and dominant with children and adults; whereas, children with low Extraversion tend to be quiet, calm, inhibited, and submissive to other children and adults. Individual differences in Extraversion first manifest in infancy as varying levels of positive emotionality. These differences in turn predict social and physical activity during later childhood and may represent, or be associated with, the behavioral activation system. In children, Extraversion/Positive Emotionality includes four sub-traits: three traits that are similar to the previously described traits of temperament – activity, sociability, shyness, and the trait of dominance. Activity: Similarly to findings in temperament research, children with high activity tend to have high energy levels and more intense and frequent motor activity compared to their peers. Salient differences in activity reliably manifest in infancy, persist through adolescence, and fade as