In this study, the researcher wanted to answer the following research question: How do K-12 assistant principals and principals develop their leadership skills and practices on the job after their pre-service programs in various school contexts? The researcher used purposive sampling, gathering participants from a state association of school principals in New England. The researcher conducted semi-structured interviews with each participant and used the Dreyfus & Dreyfus Five Stage Model of Adult Skill Acquisition (The Model) results as well as documents to support the participants' perceived skill level. Inductive analysis was used to analyze the interviews, The Model, and document examination. Then, a cross-case analysis was conducted to reveal practices school leaders have developed on the job in order to be effective leaders in their school contexts. In order to address issues of trustworthiness, researcher utilized member checking, triangulation (interviews, skill model, and document examination), coding strategy, peer review, and thick description to address credibility, transferability, dependability, and confirmability. [For the complete proceedings, see ED597786.]