Effective reciprocal communication is a vital component in forming and maintaining social relationships. Peer social play may provide a particularly important context for communicative skill development, as sophisticated negotiation and exchange are required to coordinate play. We focus on connectedness, a property of conversation referring to the topical relation between speakers’ turns, to understand how partners coordinate ideas to build a shared play experience. The proposed study will use a longitudinal secondary analysis approach to drive forward our understanding of the individual and shared influences that contribute to connectedness during peer social play. Using data from a three-wave, longitudinal study of children’s play and social relationships during the first three years of school in the UK (https://osf.io/3p4q8/), we will code connectedness from transcripts of video observations of 152 children playing in pairs at wave three (mean age 6.79 years) and model individual differences in theory of mind, emotion comprehension, and language ability from all three waves as potential predictors of connectedness. Ultimately, we hope to provide a sound theoretical and empirical basis to underpin future work on play as a context for development and enhancement of communicative competences.