A 4-year United States Office of Education prekindergarten-kindergarten series of research studies has provided data useful in predicting school success. The present study compares test scores of the Complete Assessment Battery administered before the children entered kindergarten with scores of the same children on the Metropolitan Readiness Tests at the end of kindergarten and on the Stanford Achievement Test at the end of the first primary year. Test scores of 48 boys and 55 girls were combined as age and sex differences in readiness and achievement were not statistically significant. Whole and part test scores were treated separately. The Illinois Test of Psycholinguistic Abilities, Language Quotient (ITPA-IQ) proved to be a reasonably good predictor of performance on the Metropolitan Readiness Tests, and predictability was increased by using only three ITPA subtests and the test of Visual-Motor Integration (MVI) instead of the whole ITPA battery. Performance on the Stanford Achievement Test could be predicted best by using one ITPA subtest (Auditory-Vocal Association) and the test of VMI. Throughout the study, ITPA-3 proved to be the best single predictor. (Author/NH)