Writing skills typically develop over a course of more than two decades as a child matures and learns the craft of composition through late adolescence and into early adulthood. The novice writer progresses from a stage of knowledge-telling to a stage of knowledge-transforming characteristic of adult writers. Professional writers advance further to an expert stage of knowledge-crafting in which representations of the author's planned content, the text itself, and the prospective reader's interpretation of the text are routinely manipulated in working memory.