One of the most persistent questions in the field of development is: How do parents influence the development of their child's intelligence and personality? To answer this question, one approach is for researchers to look for correlations between the way the parents behave toward the child and the way the child turns out—child outcomes. Very often, these correlations are then used to infer environmental effects on the child: the environment provided by the parent is assumed to be the cause of the child outcomes. For example, if the parents have a good vocabulary and often engage the child in conversation, and this child does better in school, it is assumed that the parents' verbal behavior stimulated intellectual growth in the child. If the parents' method of discipline is harsh or inconsistent and the child is found to be disruptive or aggressive, then this is because the parents failed to teach (by instruction or example) self- control or the proper social norms. In other words, parental treatment is usually considered to be an "environmental influence" that has the capacity to shape the children's development.