This is a summary of the original research paper, but it's an accurate one. Impulsivity is probably the most easily trained of behaviors associated with attention deficit hyperactivity disorder. In this study, high impulsivity was most highly correlated with a "lax" parenting style with inconsistent consequences for misbehaviors. Families with high emotional reactivity on the part of the parents (got very upset at children) were also at greatest risk for having children with impulsive behaviors.
The most important point, though, was that children's impulsivity really decreased in response to more structured discipline (after parents received instruction). Hope this helps someone.