We utilized classroom video observations to examine the frequency and function of spontaneous communication in 112 preschool-3rd grade children with autism within 57 classrooms. Children initiated 7.53 instances (SD = 9.42) of spontaneous communication on average within a 12-minute sample, a rate of 0.69 initiations per minute. Autism features, receptive and expressive language, and adaptive functioning were associated with communication rate. A 4-factor model of spontaneous communication functions exhibited the best relative and absolute fit to the data. Findings highlight, and begin to explain, variability in spontaneous communication children used in classrooms, link individual developmental characteristics to communicative initiations, and provide evidence for conceptualizing and measuring spontaneous communication in learners with autism across classroom activities. Implications and future directions are discussed.