Multilevel Drupal Teams or Whom to fire first?

The session will be about challenges in multi-level Drupal teams, which include Juniors, Mid and Seniors at the same time.  I will sketch some paths and add Drupal milestones that I used to evaluate when a person has grown or it's interests have changed, thus offer it more challenging tasks. I will speak about my experience and the teachings that I took from it, also will involve the audience in order to have more points of view on the topic.