To understand a child's portfolio selections and bring a sophisticated level of analysis to children's writing, teachers need to possess a working knowledge of what research tells them about the nature and development of children's writing. This text addresses the primacy of teacher knowledge in the portfolio process. it seeks to answer questions such as: What do we need to know in order to assess the personal narratives, stories, and non-fiction pieces children select for their portfolios? How can progress be marked in children's stories or non-fiction reports? What do teachers need to know to assess the conventions of spelling, punctuation, and handwriting in their selected pieces? How can children's self-assessment insights and goals for future learning be assessed? The author makes the case for the collaborative portfolio - one that merges the selections, reflections, and goals of both child and teacher. In the collaborative portfolio model, the child retains ownership while the teacher creates a school-based portfolio which contains the child's assessment decisions as well as the teacher's selections, reflections and goals. The book takes the stance that if portfolio assessment is to stand as a viable alternative to standardized measures, it is essential to capture the insights of both the child and the teacher in order to illuminate the full extent of a child's learning - past, present, and future. The author provides a case-study of the collaborative portfolio of a third-grade student, following his progress through grades four and five. Research findings are presented in conjunction with the child's writing record, writing samples, excerpts from his interviews and surveys, and other materials. Additional analysis of work from both younger and older children illustrates the development of writing across a broad age range.