This study compared the relative contribution of earliest assessment of preschool children's context-specific problem behaviors with subsequent observations of those behaviors for the prediction of later academic and sociobehavioral performance in first grade. Using a nationally representative sample of low-income children from the Head Start Impact Study (N = 3,827), children's problem behaviors in 22 classroom situational contexts were assessed annually through 2 years of prekindergarten, kindergarten, and first grade. Results from a two-stage analytical approach support the use of earliest assessment as a suitable strategy for the identification and intervention of children's classroom problem behaviors, where subsequent observations did not increase predictive accuracy over earliest assessment alone. Implications are discussed for assessment theory and practice.