One objective of the International Study of Achievement in Written Composition was to develop an instrument that could explore the relationships between instructional variables and educational results. Three levels of specificity were aimed at: (1) broad and general characteristics of the instructional process; (2) specific dimensions of native language instruction; and (3) instructional variables. A review of the literature on critical variables in writing instruction revealed that prewriting activities (activities focusing student attention on the questions of how to organize a text and how to generate ideas, on problem solving categories, and on rules for systematiclly treating a subject) clearly had positive effects on writing. Those variables with doubtful effects included the workshop/writing lab approach, group work, the reading models approach, the methods that lean heavily on individual conferences between teacher and student, the individualized approaches, and the approach in which the writing frequency is stepped up without special assistance. The questionnaire that was finally developed contained questions on prewriting instruction, types of tasks to be written, characteristics of writing instruction, materials and aids, and feedback. (The questionnaire is appended.) (HOD)