The reliability of four measures of written expression was examined (total words written, mature words, words spelled correctly, and letters in sequence). Subjects included elementary-age students in several school districts, some of whom were learning disabled. Results revealed high coefficients for test-retest reliability, parallel-form reliability, split-half reliability, and interscorer reliability. Further, the reliability coefficients for total words, words spelled correctly, and letters in sequence were consistently superior, demonstrating significant precision in measurement. Two implications are drawn from the research: (1) high reliability estimates of the measures of written expression provide a necessary basis for the determination of their validity; and (2) the research assures teachers and educational professionals using formative evaluation measures that such procedures are accurate and stable. (Author/GK)