This paper reports the results of a study which examined the longitudinal relationships between young children's classroom behavior and their performance on achievement tests. Subjects were 235 children who made up the first cohort to attend kindergarten in the public schools of North Carolina. Data were collected at four points: at the beginning and end of kindergarten, and at the beginning and end of grade one. Subjects' behavior factors of extraversion, social behavior, and task orientation were measured at the four points by the Schaefer-Aaronson Classroom Behavior Inventory. Their achievement performance at the end of grade one was measured on five subtests of the Stanford Achievement Test (word reading, paragraph meaning, vocabulary, word study skills, and arithmetic). Among the results, Pearson product moment correlations and multiple regression analysis revealed that of the three independent variables, task orientation had the strongest and the most consistent relationship to achievement. The relationship of extraversion to achievement, while strong at the beginning of the first grade, decreased by the end of the year. Discussion of these findings centered on the assertion that children low on reading achievement at the end of first grade are at risk at this time of being less extraverted, more hostile in their social behavior and less task oriented than when they began kindergarten. (Author/MP)