We develop a conceptual framework for understanding and predicting teacher shortages at the state, region, district, and school levels. We then empirically examine how teacher shortages vary geographically and by subject using data on unfilled teaching positions in Tennessee traditional public schools during Fall 2019. We find that teacher staffing challenges are highly localized, causing shortages and surpluses to coexist. Aggregate descriptions of staffing challenges mask considerable variation between schools and subjects within districts. Schools with fewer local early-career teachers, smaller district salary increases, worse working conditions, and higher historical attrition rates have higher vacancy rates. Our findings illustrate why viewpoints about, and solutions to, shortages depend critically on whether one takes an aggregate or local perspective.