A study aimed to increase understanding of how different writing-to-learn tasks invite the ways in which students construct meaning in writing from sources. The tasks used, writing either a report or a problem-based essay, required students to integrate prior knowledge with information from six textual sources in order to construct their own texts. Fifteen undergraduates, enrolled in a seminar on European history, were randomly assigned to one of two task conditions. Comparisons were made between the ways in which the two groups interpreted the tasks they were given, as well as how they organized and selected content from the sources. All students provided think-aloud protocols and reading-writing logs. Students' essays were analyzed for top-level structure, origin of information, and appeals to authority. Comparisons were also made to examine possible differences in learning associated with the two tasks. Analyses showed that the groups differed significantly in their interpretations of the two tasks and in their approaches to structuring textual information. Analyses also revealed that students writing problem-based essays included significantly more content units in their essays than students writing reports. Results suggest that authority can be linked to the transformations writers make in composing from sources as they interweave content from prior knowledge with source information and restructure meaning. Authority can also come from writers' awareness of how to apply their knowledge flexibly and effectively in a given rhetorical situation. (Two figures and 6 tables of data are included; 90 references are attached.) (Author/SR)