An effective teacher is the most important school-based determinant of education outcomes. Therefore it is crucial that school districts recruit and retain high-quality teachers. This is increasingly challenging given that the supply of teachers has been greatly affected by high early to mid-career turnover rates, annual retirements of longtime teachers, and a decline in students opting for a teaching career. At the same time, many factors are increasing the demand for teachers, including shrinking class sizes, the desire to improve diversity, and the need to meet high standards. In short, the demand for teachers is escalating, while simultaneously the supply of teachers is faltering. This report finds that the teacher pay penalty is bigger than ever. In 2015, public school teachers' weekly wages were 17.0 percent lower than those of comparable workers--compared with just 1.8 percent lower in 1994. This erosion of relative teacher wages has fallen more heavily on experienced teachers than on entry-level teachers. Importantly, collective bargaining can help to abate this teacher wage penalty. Some of the increase in the teacher wage penalty may be attributed to a trade-off between wages and benefits. Even so, teachers' compensation (wages plus benefits) was 11.1 percent lower than that of comparable workers in 2015. The following are appended: (1) Summary of the data used in this analysis; (2) A table with estimated public school teacher weekly wage penalty, 1979-2015; and (3) A table with public school teacher and non-teacher college graduate weekly wages, by state.