This study tested the hypothesis that curriculum type (Montessori and constructivist) moderates the impact of temperament (specifically activity level and attention-span/persistence) on the classroom behavior of 3- to 5-year-old children. Mothers enrolled in Montessori and constructivist preschools filled out the Colorado Childhood Temperament Inventory. The children's teachers filled out the Preschool Behavior Questionnaire and the Preschool Adjustment Questionnaire. A near-significant trend suggested that temperamentally active boys were more likely to be perceived by their teachers as having behavior problems if they were enrolled in Montessori programs than if they were enrolled in constructivist programs. There was no such trend for girls. There was no evidence that temperamental attention-span persistence moderated the impact of curriculum type on either boys' or girls' behavior. The findings thus give modest support to the notion that parents should be advised to select constructivist early childhood programs especially for boys who are temperamentally predisposed to be highly modifying their teaching practices to better accommodate the needs of these children active. In addition, directors and teachers in Montessori programs may consider modifying their teaching practices to better accommodate the needs of these children.