Writing can be viewed as a recursive process involving both cognitive and metacognitive processes. Task, environment, individual cognition and affective processes all impact on producing written text. Recent research on the development of metacognition in young children has highlighted social constructivist and socio-cultural factors. Metacognition is seen as facilitated through collaborative tasks and through talk. This study investigated the peer construction of metacognition in 5-7-year-old children engaged on collaborative writing tasks. Six year 1 and year 2 classes were involved in the project (n = 172). 25 h of video observation data, teacher and researcher reflections and structured field notes were analysed qualitatively using ATLAS ti software. The written texts produced in these sessions were analysed using a qualitative content analysis, looking specifically for evidence of the process of text construction and metacognition. The findings provide evidence of young children's ability to engage in metacognitive talk and to use metacognition intentionally in the co-construction of written texts. The relationships between children and their talk partners mediated the effect of pre-determined ability in literacy. Teachers' direct questioning aimed at reflection on the writing process did not always support metacognitive dialogues. Drawing on recent models of metacognition and writing the paper highlights the role of social factors in developing metacognition and illustrates the ways in which young children negotiate task demands during shared writing tasks. (Contains 4 tables.)