The first purpose of this study was to examine the relationships between changes made during the development of written instruction and the effectiveness of the materials when presented to students. For this purpose, the Written Instruction Stylistic Evaluation was used to assess the comprehensibility of passages before administration of the passages to students. The second purpose of this study was to assess the degree to which the rewriting efforts of experienced writers are successful in improving the comprehensibility of written instruction. The instrument for this study was formulated by translating modern concepts of reading comprehension and instructional development into 12 guidelines for writers in the form of anchored rating scales. Regression equations predicted much of the variance in the student scores. Thus, this study found strong predictive relationships between the changes made during instructional development and the students' success in using the resulting materials. However, the optimum regression equation was different for each outcome measure. (JAZ)