Researchers studying curriculum-based measurement of written expression have used a variety of writing prompt types and durations when establishing criterion validity of these tools. The purpose of this study was to determine through meta-analytic procedures whether any prompt type or duration was superior to others in terms of criterion validity. The literature search returned 24 articles (N = 24) that met our inclusion criteria. Included studies examined criterion validity for a variety of prompts: picture, story starters, expository, text copying, picture-word, and picture-story. These studies also reported criterion validity for writing durations ranging from 1.5 to 10 minutes. Results indicated no clear trends in criterion validity for prompt or duration. We provide suggestions for practitioners considering the use of CBM in written expression.