The nature and function of proposals in collaborative writing of primary school students was studied from a sociocultural, interactional perspective, using data from 33 writing events in the context of inquiry learning. Five main targets of proposals were identified: content, procedure, translation, text structure and layout. We demonstrate how proposals are designed in different declarative and interrogative constructions. The objective of a proposal appears to be related to both the syntactical design, and the ways in which participants respond to proposals. Proposals for content and translation generate extensive discourse, in contrast to procedural proposals. Writing down the agreed words or sentences occurs in various sequential positions and consequently performs a different function in the joint construction of text. The results enhance our understanding of how primary school students collaboratively write texts.