School-aged and adolescent children continue to demonstrate improvements in how they integrate and comprehend real-time, auditory language over this developmental time period, which can have important implications for academic and social success. To better understand developmental changes in the neural processes engaged during language comprehension in this age group, we use electroencephalography to investigate how 8-9 year old, 12-13 year olds, and adults process semantics and syntax in naturally paced, auditory sentences. Participants listened to semantically and syntactically correct and incorrect sentences and were asked to complete an acceptability judgment task. When processing a semantic error, developmental differences were observed in theta, but not the N400, suggesting that the N400 may be too gross a measure to identify more subtle aspects of semantic development that occur in the school years. For the syntactic task, errors resulted in a larger P600 and greater beta decrease than correct sentences, but the amplitude and location of the P600 and amplitude of beta decreases differed as a function of age, suggesting specialization of syntactic skills is ongoing through adolescence. The current findings shed new light on the development of the neural oscillations supporting language comprehension and suggest that the neural substrates underlying semantic processing reach adult-like levels at a younger age than those underlying syntactic processing.