As the debate in trait theory faded, a growing interest arose that helped to shed more insight on leadership, specifically the differences between leadership and management. For some time, of course, experts made no distinction between the two. They combined both leadership and management under the rubric of "classical management."
Under classical management, the topic of leadership was skewed towards three areas: standardization, specialization, and functionalization. What is known today as the "people side" of management was emphasized very little. The very qualities of a manager were assumed to be the very same ones for a leader: analytical, logical, organized, methodical, consistent, orderly, and task oriented.
The lack of distinction is based on the theories of classical management thinkers like Frederick Taylor, Henri Fayol, Chester Barnard, and Lyndall Urwich. Such thinkers emphasized planning, organizing, controlling, and commanding with little consideration of the psychological and behavioral factors behind such activities. Most came from a scientific management and classical management perspective; eventually the trait and classical management perspectives showed their inadequacies by ignoring behavioral aspects.
Today, experts generally agree that a marked difference exists between leadership and management. The characteristics are quite clear. In On Becoming a Leader , Warren Bennis provides an excellent list of distinctions between the two. Some major distinctions include administering versus innovating ; maintaining versus developing; controlling versus trusting; and, perhaps most importantly, doing things right versus doing the right things.  Other top leadership experts agree, including Max De Pree, Stephen Covey, and Barry Posner.
 Warren Bennis, On Becoming a Leader , Perseus Books, Reading, MA, 1989, p. 45.