The high rate of students taking developmental education courses suggests that many students graduate from high school unready to meet college expectations. A college readiness screener can help colleges and school districts better identify students who are not ready for college credit courses. The primary audience for this guide is leaders and staff at colleges that are seeking to revise or evaluate their screening methods or to develop a college readiness screener if they do not already have one. This guide describes core ideas for colleges to consider when developing a screening tool for estimating college readiness. A key focal point within the guide is a discussion of ways to improve how well a screening tool can identify individuals needing remedial or developmental education, along with key considerations that a user or developer of such a tool must address. This guide discusses the following steps: (1) Creating an operational definition of success and college readiness; (2) Selecting potential predictors of college readiness; (3) Prioritizing types of classification error; (4) Collecting and organizing the necessary data; (5) Developing predictive models; and (6) Evaluating the screening results and selecting the final model. The guide includes the appendix: Methodological guidance and resources.