This article investigates children's evaluation/selection of ideas in writing-related tasks. The critical dimension being considered was to what extent the communicative goal that defines argumentation establishes basic criteria with which children decide whether to include counterargument in a text. Data analysis focused on participants' decisions and, most important, the rationales they present for their decisions. Two constraints seem to drive evaluation/selection processes. First, the content constraint, whereby a writer focuses on agreement with the idea itself; second, the rhetorical constraint, defined as a writer's perception of an idea's value in increasing the acceptability of his or her point of view. Counterargumentation must be perceived as a valuable rhetorical strategy if specific counterarguments are to be incorporated into a text; otherwise, counterargumentation remains part of the process of selection/evaluation without becoming explicit in the product of such a process—the text.