At least half of states administer or are developing kindergarten entry assessments. In fall 2017 the Illinois State Board of Education began requiring teachers to report data on every child's skills at kindergarten entry using the Kindergarten Individual Development Survey, which was adapted from a California kindergarten assessment. This study analyzed the psychometric properties of the 14 required items on the survey after its first statewide administration. It examined average skills and the variation in skill levels at kindergarten entry, as well as their differences across child subgroups (children eligible for the national school lunch program and those not eligible, boys and girls, English learner children and non-English learner children, children eligible for an individualized education program and those not eligible, and children of different races/ethnicities) and school poverty levels. And it interviewed teachers and principals about barriers in administering the survey and suggestions for improvement. The study used data from the fall 2017 Kindergarten Individual Development Survey, state student records, the federal Common Core of Data, and interviews with nine kindergarten teachers and nine principals. The study team analyzed the quantitative data using psychometric and regression analyses and analyzed the interview data by coding interview transcripts. [For the report, see ED599357; for the appendixes, see ED599358; and for the brief, see ED599364.]