Prekindergarten students (n=1,137) in an ethnically and socioeconomically diverse urban public school took a kindergarten diagnostic assessment in September prior to entry into the regular kindergarten program. The assessment was a pilot version of a longer instrument that had been used at the school for several years. Results were used for placement, program planning (class size and multiage grouping), remediation, instructional improvement, and counseling with parents. The results of the diagnostic assessment were evaluated to determine differences in student readiness for kindergarten by gender, ethnicity, socioeconomic status, and English language proficiency. The objective of this analysis was to determine the reliability and validity of the newer, abbreviated version of the kindergarten assessment and its usefulness in making decisions about individuals and groups of students. This paper provides examples of item domain goals and objectives, identifies items that could be useful to equate with other prekindergarten assessments, examines differences in skill attainment for male and female children from ethnic minority groups not identified as Limited English Proficient (LEP) or English Language Learners (ELL) and provides comparisons of several approaches for psychometric evaluation of test items including the transformed item difficulty index, normal curve equivalents, item characteristic curves, and two-parameter Rasch modeling. Implications for assessment and instruction of children from different cultural and ethnic backgrounds are discussed as well as implications for addressing differences in skills attainment for male and female children as they progress through school. Three appendixes contain a correlation matrix for three assessments, a table of sample norms, and a table of normal curve equivalents. (Contains 8 tables, 12 figures, and 58 references.) (Author/SLD)