Investigates the effect of the first-grade classroom environment on the shy behavior, aggressive behavior, and concentration problems of 609 children in 19 East Baltimore public schools. First-grade classroom environment was assessed in terms of dominant pattern of classroom achievement and behavior. Structured teacher ratings assessed child shy behavior, aggressive behavior, and concentration problems at the end of first grade. Children in low-achieving classroom environments had significantly higher teacher ratings of shy behavior and aggressive behavior than children in mixed-achieving or high-achieving environments, even after controlling for potentially confounding child characteristics and classroom behavior environment effects. Analyses controlling for child characteristics and classroom achievement environment effects indicated that children in poor-behaving classroom environments also had significantly higher teacher ratings of shy behavior than children who were not in poor-behaving environments. Subgroup analyses indicated that repeaters in mixed-achieving environments had significantly higher levels of shy behavior compared with nonrepeaters, and repeaters in poor-behaving environments had significantly higher levels of aggressive behavior compared with nonrepeaters. Implications for prevention research are discussed.