British students in four age groups--4 to 5, 7 to 8, 11 to 12, and 15 to 16 years old--were observed in their classrooms in order to explore the relationships among the learner, knowledge, and thinking, and the role that writing plays in what is learned. In the infant classroom, writing was quite visible in the form of labels, questions, sentences, word and number lists, personal stories, classmade books and charts, and published books. In the junior school classroom, which included 8 and 11 year olds, writing was not as visible as it had been in the infant classroom, since movements in the classroom were more limited and looking at other people's writing was not acceptable. In the secondary school classroom writing became the major means of demonstrating private knowledge and became increasingly separated from direct experience. These changes resulted in students parroting information back to the teacher. These observations suggest that writing should be considered as simply one form of knowledge manifestation, and teachers should not only recognize the difference between process and product but use student writing as a gauge of thinking strategies. Examples of children's writing illustrating various aspects of the learning process are included. (DF)