This report in the series “The Perfect Storm in the Teacher Labor Market” describes the challenges schools face in staffing themselves, both as a consequence of the teacher shortage and further contributing to it. It shows that a high share of public school teachers are leaving their posts: 13.8 percent are either leaving their school or leaving teaching altogether, according to most recent data. It also shows that schools are having a harder time filling the vacancies that turnover, attrition, and other factors (like increasing student enrollment or broadened curriculums) create. The share of schools that were trying to fill a vacancy but couldn’t tripled from the 2011–2012 to 2015–2016 school years (increasing from 3.1 to 9.4 percent), and in the same period the share of schools that found it very difficult to fill a vacancy nearly doubled (from 19.7 to 36.2 percent). These difficulties are also shaped by a dwindling pool of applicants to fill vacancies.