Leading research argues the distinct importance of earliest detection of childhood behavior problems and the value of discovering subsequent change patterns as children transition through the early education years. This study examined the relative contributions of earliest assessments of children's problem behaviors as compared to the changes in those behaviors over time for the prediction of important later outcomes. Focusing on the representative national sample from the Head Start Impact Study (n = 3,827), classroom behavior problems were assessed across 4 years spanning prekindergarten through first grade. Individual child indices were derived in multilevel growth modeling to reflect initial assessments and subsequent change patterns. These indices were thereafter applied in multilevel logistic regression and receiver operating characteristic curve analyses to predict later academic and social difficulties. Both children's initial assessments and their transitional changes proved to be good predictors of most outcomes, where the accuracy for initial assessments and transitional changes was effectively equivocal. The evidence clarifies that initial assessment of behavior problems is sufficient to predict later outcomes; additional assessments did not augment forecasting accuracy nor did the combination of both initial assessment and information about subsequent change improve accuracy. Implications are discussed for assessment theory and practice. [This research was conducted with the cooperation of the U.S. Department of Health and Human Services, Administration for Children and Families.]