A study was conducted to determine whether counting correct word sequences is a valid measure of written expression for use in a formative evaluation system for elementary students. A correct word sequence was defined as two adjacent, correctly spelled words that were acceptable within the context of the phrase to a native speaker of the English language. Written expression samples from 50 students in grades 3 through 6 were scored in terms of correct word sequences to investigate (1) the consistency among scorers using the procedure, (2) the typical performance levels of students in these grades on this measure, and (3) the validity of this measure relative to criterion measures of written expression. Analyses revealed that the average inter-scorer agreement was 90.3%. Average scores for students in grades 3 through 6 ranged from 27.3 at grade 3 to 58.8 at grade 6, with an increase of about 10 for each successive grade level. Correlations between correct word sequences and several criterion measures, including a holistic rating, were very high, leading to the conclusion that correct word sequences were highly representative of appropriate writing and that counting them is a valid and reliable measure of written expression. (HOD)