This technical manual provides an overview of the Mosaic™ by ACT®: Social Emotional Learning Screener. The Mosaic by ACT: Social Emotional Learning Screener (hereafter referred to as the Screener) assesses the social emotional skills of students in elementary school (Grades 3-5), middle school (Grades 6-8), and high school (Grades 9-12). Each assessment also measures students' perceptions of school climate. While the full-length Mosaic™ by ACT®: Social Emotional Learning Assessment provides a thorough assessment of students' skills and perceptions of school climate, complete with comprehensive reporting, the Screener provides a quick overview of students' skills in each area. The Screener can be completed online in 5-7 minutes. It also includes two aggregate-level reports on students' social emotional skill and school climate levels. This manual contains an overview of the skills assessed and the various item types used, as well as a description of how the assessment is scored and how scores are reported. In addition, it reports a summary of reliability and validity findings for each version of the assessment.