This couldn't be further from the truth. When lids are flipped, no learning can take place! Parents can't teach and kids can't learn when the rational brain is offline. Messages about hitting, or yelling, or fighting with your brother, or doing your homework do not penetrate in the heat of the moment.
There is something that parents can teach, however, and they can teach it the very best way -- by example. By modeling. By demonstrating. By showing the child that calming down is mandatory before problem-solving can occur. They can show the child they care enough to regather before they act or speak disrespectfully. They can show they respect themselves enough to meet their needs for safety and calm in the moment. They can trust that the model of their actions will teach more than any fiery lecture could. In fact, when parents are able to calm down and reconnect, the closeness and trust that result will make the child more willing to listen to whatever lessons they later decide to teach, and be a powerful piece in helping the child learn to regulate his own emotions.