Whereas there has been strong advocacy of the value of writing for learning in science, the role of student planning in this approach and the relationships between planning, writing, and learning have been underresearched. Our mixed method study aimed to address this issue by seeking to identify quantitative differences in learning outcomes between two groups of students exposed to varying degrees of planning activities in writing-to-learn experiences. We also identified differences in learning outcomes between a group of students with two writing experiences and a group with one writing experience. Results indicate that students with planned writing activities did not score significantly better on conceptual questions as a group than students who had delayed planning experiences. Students with two writing experiences as opposed to one also scored significantly better as a group on answering conceptual questions both immediately after the writing experience and on a test 8 weeks after the unit. The difference in writing treatment initially significantly affected males compared with females but this effect disappeared with further opportunities to write. Students' comments provide support for using nontraditional writing tasks as a means to assist learning, particularly when the focus is on an audience different from the teacher. In reporting on different learning outcomes for the two groups, we consider various implications including identification of some key conditions for student writing to serve learning.