The research reported here employed a multiple-case study methodology to assess the online cognitive and metacognitive activities of 15-year-old secondary students as they read informational texts and wrote a new text in order to learn, and the relation of these activities to the written products they were asked to generate. To investigate the influence of the task, students were required to perform two different tasks which differed in complexity and familiarity. The first task was reading a single text and making a written summary of it, while the second consisted in reading two texts and making a written synthesis of them. To gather information about how students construct meaning from informational texts, we asked students to think aloud as they read and wrote in order to provide us with information about their comprehension and composition processes. We also examined their reading and writing activities during the tasks. The results show that to a large extent secondary school students lack the cognitive and metacognitive processes that would enable them to make strategic use of reading and writing. They also show that, although there are no major differences in the way secondary school students tackle these different tasks, those who create the most elaborate products evidence a more recursive and flexible use of reading and writing. The most obvious conclusion as far as the repercussions of these findings are concerned is that there is an urgent need for work on tasks of this kind in the classroom.