In this report, we perform an analysis of kindergarten readiness in Illinois and relate it to students' third grade academic achievement. We study two cohorts of Illinois kindergarteners and follow them into third grade using data provided by the Illinois State Board of Education (ISBE). We summarize our key findings below: (1) Disparities appear larger in third grade than in kindergarten; (2) Overall, KIDS predicts performance on standardized achievement tests in Grade 3; and (3) Kindergarten readiness alone does not guarantee academic success, especially for Black and Hispanic/Latino students and students who are FRPL-eligible.