Working memory has been proposed to account for the differential rates in progress young children make in writing. One crucial aspect of learning to write is the encoding (i.e., integration) and retrieval of the correct phoneme-grapheme pairings, known as binding. In addition to executive functions, binding is regarded as central to the concept of working memory. To test the developmental increase in binding ability and its comparative influence on writing, an experimental study assessed 5- and 6-year-olds' accuracy in retaining and retrieving bound audio-visual information alongside measures of verbal and visual complex working memory span (i.e., central executive functions), and transcription skills (i.e., alphabet and spelling). Results demonstrated an age-related increase in the ability to bind, and that binding had significant associations with working memory and early writing ability, but once binding and age were controlled for it was verbal working memory that made an independent contribution to individual differences in writing performance. Although the contribution this paper made was through an exploration and expansion of theoretical ideas within writing research, it is likely to make an important practical contribution to instruction in the future both at the level of transcription and text generation as writers develop those skills.