Summary: The nature of mathematical argumentative writing (MAW) is relatively understudied, particularly in the context of early childhood. While much of the literature on MAW, and mathematical argumentation in general, has focused on the manner in which procedures and warrants are sequenced, the present study focused on the grammatical resource of mathematical detailing. Mathematical detailing involves the linguistic operationalization of given information within and across the sequencing of warrants to support a mathematical claim. The present study examined the effect of varying the complexity of the given information in two similar tasks on how children used given information in their mathematical writing. Findings indicate that increasing the complexity of the givens can encourage many children to operationalize the given information, as well as provide insight into children’s communicated conceptions of the mathematics at hand.