Leadership, for the purposes of this discussion is influence. A leader has followers. It's that simple. You can claim to lead and teach leadership but followers, influence, or clients with followers or influence prove your claim. Everyone influences others for good or bad in some ways; maybe it's just your children or your neighbors. Everyone can think of times where they encouraged others to see or do things a particular way. That's leadership.
Over time, you begin to move up the ladder. You prove your leadership. As you become a director or vice-president, the game changes. You no longer lead people who sell, engineer, design, develop or serve customers. You lead people who lead.
How do you help your new or emerging leaders? Why should you help them? You really need them to help you. They need to make their team productive and support the overall goals of the group or company. But that requires they deliver effective leadership in a number of situations or contexts. While they may understand the context they came from, as a salesperson, engineer, or whatever their job was, they now have to handle many more and different situations. In addition to their team, they also need to influence their peers, suppliers, and outside resources. They even need to learn how to use their knowledge and relationships to inform you and help you be a better leader. How can you teach them to lead in a single situation, much less all of these situations at the same time?