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. Relationships were examined in two cohorts of 4,462 and 4,602 students. After controlling for a number of important variables, we found significant relationships between social and behavioral readiness in kindergarten and all three school outcomes. Specifically, by third grade, students assessed as not socially and behaviorally ready in kindergarten were significantly more likely to be retained in grade, receive services and supports through an IEP or 504 plan, and be suspended or expelled. These results were consistent across both cohorts of students. In addition, boys were significantly more likely than girls to be assessed as not socially and behaviorally ready for school and to experience all three academic problems. (author abstract)