This is a good question. Mac Lake explains that fundamentally the process is the same, but the focus is different.
Discipleship I learn to live like Jesus
Leadership development I learn to lead like Jesus
Discipleship is primarily about character
Leadership development is primarily about competencies
Discipleship is about leading self
Leadership development is about leading others
Discipleship is about cultivating intimacy with God
Leadership development is about cultivating influence with people.
What other distinctions would you add to this list?