This dissertation examined how anxiety levels and social competence change across the course of early elementary school, as well as how individual differences at the transition to kindergarten may influence these trajectories. Previous research has supported unidirectional relations among anxiety and social competence, but few studies explore how inter- and intra-individual changes in social competence and anxiety may be related across time. From a developmental perspective, studying these trajectories following the transition to kindergarten is important, as cognitive and emotion regulation capacities increase markedly across kindergarten, and the relative success with which children navigate this transition can have a bearing on future social and emotional functioning across elementary school. In addition, given gender differences in anxiety manifestation and social competence development broadly, gender differences were also examined in an exploratory manner. Data from parent and teacher reports of a community sample of 291 children across kindergarten, 1st, and 2nd grades were analyzed. Results from bivariate growth models revealed steeper increases in anxiety, relative to peers in the sample, were associated with steeper decreases in social competence across time. This finding held after controlling for externalizing behavior problems at each time point, which suggests that relations among anxiety and social competence may be independent of other behavior problems commonly associated with poor social adjustment. Temperament variables were associated with changes in social competence, such that purportedly "risky" temperament traits of higher negative emotionality and lower attention control were associated with concurrently lower social competence in kindergarten, but with relatively steeper increases in social competence across time. Temperament variables in kindergarten were unrelated with changes in anxiety across time. Gender differences in relations among anxiety in kindergarten and growth in social competence also were revealed. Findings for teacher and parent reports of child behavior varied. Results are discussed with respect to contexts that may drive differences between parent and teacher reports of child behavior, as well as key developmental considerations that may help to explain why kindergarten temperament variables examined herein appear to predict changes in social competence but not changes in anxiety levels.