In this study a holistic approach was used to evaluate students' writing skills in a high school that is part of a residential treatment program for adolescents. Prior to this there was no school-wide method of evaluating writing skills. Students were asked to produce spontaneous writing samples in response to the same standardized prompt in the fall and spring of the 1990-91 school year. A total of 740 writing samples were scored by faculty members at the school. Results indicated good interrater reliability and significant gains in writing skills for students during the year. The criteria used to score the writing samples developed into an instructional tool for teaching writing skills. Applications of the assessment process and criteria to student monitoring and classroom instruction are described.