Staffing classrooms with effective teachers remains a persistent policy challenge in the U.S. Teaching positions requiring STEM expertise are particularly difficult to fill. Scholars have identified similar trends in other industrialized nations. Yet, limited research examines international comparisons of the causes and consequences of staffing challenges. We use the 2015 Trends in Mathematics and Science Study to track teacher staffing difficulties in 27 countries. We find substantial variation across countries in the proportion of principals reporting difficulties filling STEM positions, with U.S. schools mirroring international averages. We also find consistent relationships between lower math and science achievement and attending a hard-to-staff school.