A research project was undertaken to (1) identify the major cognitive processes involved in expository writing, (2) test a model of the organization of those processes, and (3) identify teachable aids that could be used by poor and average adult writers to improve their writing skills. Subjects were expert and novice student writers at Carnegie-Mellon University in Pittsburgh, Pennsylvania. The research method employed was that of protocol analysis, with each student being asked to think aloud as he or she performed writing tasks. The resulting tapes were analyzed to discover the cognitive processes involved in writing and to develop a model of composition. The findings suggest the following: (1) there are important differences in the ways expert and novice writers handle the writing process, (2) many of the strategies employed by expert writers are teachable, and (3) one of the most promising areas for improving students' writing is in the art of planning. (Charts, tables of data, and excerpts from student protocols are appended.) (FL)