Social skills and vocabulary are important areas of development involved in early reading achievement, yet little attention has been given to understanding the dynamic associations among them during the elementary years. This study examined the relations among three dimensions of social skills-cooperation, assertion, and self-control-vocabulary and developing reading comprehension (RC) skills in a longitudinal sample of first graders (n = 468). Using Structural Equation Modeling, reciprocal effects were observed between vocabulary and RC as well as direct effects among social skills, vocabulary, and RC after controlling for the influence of problem behaviors. This study highlights the reciprocal nature of students' vocabulary and RC skills as well as provides preliminary evidence suggesting that social skills play a role in developing vocabulary and RC skills, and further, vocabulary and RC skills play a role in social development during middle childhood. Implications for policy and practice are discussed.