The purpose of the study was to investigate the effectiveness of a brief and feasible universal screener for kindergarten readiness for predicting follow-up outcomes in first grade. Participants included kindergarten and first-grade teachers and students from 6 urban elementary schools. Students included slightly more males than females (54%; 46%), the race/ethnicity of the students was predominantly African American (74%) or White (23%), and 36% of students qualified for free or reduced lunch. Data included in this study were collected for children in the fall (October) of their kindergarten year and the Spring (April) of their first-grade year. Kindergarten teachers completed single-item ratings of student readiness as well as full-scale ratings of student behaviors and academic competence. Students also completed a standardized academic achievement test. Main findings from this study include that the single-item screener continued to predict negative academic and social behavior outcomes at a follow-up 18 months later. The percentage of unique variance explained by the readiness items was significant and, in the majority of cases, remained significant even after the baseline variables were entered into the analyses. Children rated poor in their academic readiness were over 9-10 times as likely to have low reading performance at the end of their first-grade year. Furthermore, children rated as poor in their behavior readiness were at over 6 times greater risk for low prosocial and high disruptive behavior teacher ratings in first grade. The screener could be used to screen for children low in readiness in order to provide supports and monitoring for early intervention. Kindergarten entry is a critical time to screen children and support them in developing skills to ameliorate deficits and build essential early academic and social behavior skills. Impact and Implications: This study highlights the importance of screening children for their readiness for kindergarten. By determining who is not academically and/or socially ready for kindergarten, we can provide instructive and supportive strategies to teach and support children who need it as early as possible.