Educators need accurate assessments of preschool cognitive growth to guide curriculum design, evaluation, and timely modification of their instructional programs. But available tests do not provide content breadth or growth sensitivity over brief intervals. This article details evidence for a multiform, multiscale test criterion-referenced to national standards for alphabet knowledge, vocabulary, listening comprehension and mathematics, developed in field trials with 3433 3-5 1/2-year-old Head Start children. The test enables repeated assessments (20-30 min per time point) over a school year. Each subscale is calibrated to yield scaled scores based on item response theory and Bayesian estimation of ability. Multilevel modeling shows that nearly all score variation is associated with child performance rather than examiner performance and individual growth-curve modeling demonstrates the high sensitivity of scores to child growth, controlled for age, sex, prior schooling, and language and special needs status. (Contains 6 figures and 4 tables.)