This is the third National Assessment report on the writing of children aged 9, 13, and 17, and young adults. The three exercises used in the writing assessment were: Age 9: The Forest Fire Exercise; Age 13: The Famous Person Exercise; and Age 17: The Famous Person Exercise. An exercise for young adults (Adults: The Commissioner Stroud Letter) required them to write formal letters to public officials expressing a viewpoint on an issue. The report contains separate chapters for each age group: Chapter 2 describes the essays written by 9-year-olds; Chapter 3 reports on 13-year-olds; and Chapters 4 and 5 describe 17-year-olds and young adults, respectively. Each chapter begins with an introductory statement about particularly important aspects of the essays that age group wrote. Chapter 6 discusses The Differences between 9's, 13's, 17's and Adults. The results of the four analyses (overall quality, error counts, characterization, and computer) are presented under six headings: essay length, paragraphing, punctuation and capitalization, sentence structure, agreement, and words (spelling, vocabulary and usage). Six appendixes present: Procedures for Assigning Overall Quality Scores; Kinds of Errors Sought in the Error Count Analysis; Characterizations; Computer Scoring of Essays; Sample Percentages; and Best Essays. Tables and figures illustrate the text. (Author/LS) Primary type of information provided by report: Results (Overview).