This study extended the work on curriculum-based measurement to examine the criterion-related validity of curriculum-based measures in written expression for middle school students, the differences in validity coefficients for various lengths of text, and the sensitivity of curriculum-based measures to change in student performance. Curriculum-based measures were the number of correct word sequences (CWS) and correct minus incorrect word sequences (CIWS) written in expository essays. Criterion measures were the number of functional elements in and quality ratings of student essays. Results revealed a strong relationship between curriculum-based and criterion measures.