This report, one of several prepared for a comprehensive policy study of early childhood education in Illinois, provides a technical review of the following twelve instruments for screening, assessing, and diagnosing young children's readiness for school: Brigance Diagnostic Inventory of Early Development; Brigance K & 1 Screen for Kindergarten and First Grade; Denver Developmental Screening Test; Developmental Indicators for the Assessment of Learning; Gesell Institute School Readiness Materials; Joseph Preschool and Primary Self-Concept Screening Test; McCarthy Scales of Children's Abilities; McCarthy Screening Test; Metropolitan Readiness Test; Miller Assessment for Preschoolers; Peabody Picture Vocabulary Test--Revised; and Portage Guide to Early Education, Revised Edition. For each of the instruments, information is presented about the age range of the children, the purpose of the instrument, content information, procedures for giving the test, standardization of the instrument, and measures of reliability and validity. Strengths and limitations for each instrument and sources of further information are provided. (DST)