Parents' involvement in their children's education is generally thought to affect children's academic outcomes. More recently, researchers have found that parent involvement also relates to children's externalizing behavior. The association between parent involvement and behavior problems could be negative or positive. When parents are more involved in their children's education, those children may exhibit fewer behavior problems. On the other hand, when children are exhibiting behavior problems, parents may become more involved in response. In several cross-sectional studies, researchers have found that higher levels of parent involvement were associated with lower levels of behavior problems in elementary school children. In two recent longitudinal studies, one with elementary school students and one with preschoolers, higher levels of parent involvement predicted decreases in problem behavior over time. Some researchers have noted ethnic differences in the level of parent involvement; for example, African American families have been found to experience more barriers to involvement.