Evidence-based assessment, which requires the use of reliable and valid measurement tools, is an essential component of many services that school social workers provide to promote the social, emotional, and behavioral health of students. A wide variety of psychometrically sound assessment tools exist to choose from, but it can be difficult for school personnel to identify and access the tools best suited to meet their needs. In an effort to reduce these barriers, the authors of this article provide a concise guide to free, validated measurement tools that are feasible for routine use in school settings for the most common youth mental health concerns (anxiety, depression, and disruptive behavior). The psychometric properties and other practical characteristics of 37 measurement tools are reviewed, accompanied by links to access each tool and suggestions to help social workers identify which may best fit any particular combination of the diverse goals, school settings, and student populations they serve.