In 2014-15, over 50% of kindergarten children in Baltimore City Public Schools (City Schools) did not meet benchmarks for social-behavior readiness. These include the readiness skills children need to follow directions, comply with rules, manage emotions, solve problems, organize and complete tasks, and get along with others. Social-behavioral readiness skills develop early, before children enter school, and they are essential for learning in a classroom setting. What is the impact of not being socially and behaviorally ready on children's academic outcomes? This report examines the relationships between social-behavioral readiness in kindergarten as measured by the Maryland Model for School Readiness (MMSR) and three costly school outcomes for City Schools' students through third grade: being retained in grade, receiving additional services and supports through an Individualized Education Plan (IEP) or 504 plan, and being suspended or expelled from school. The findings of this study underscore the critical importance of young children entering school with essential social-behavioral skills and the costly consequences of not being socially and behaviorally ready for students and their families, school systems, and society. The following are appended: (1) Characteristics for Cohorts 1 and 2 Original Sample Compared to Final Analysis Sample; (2) Assessment Standards and Indicators of Social-behavioral Readiness on the MMSR and the KRA; and (3) Logistic Regression Models for Students in Cohorts 1 and 2.