Researchers have posited various theories to explain supposed declines in teaching quality: the expansion of labor market opportunities for women, low relative wages, compressed compensation structures, and substituting quantity for quality. We synthesize these previous theories and expand on the current literature by incorporating a useful comparison group: the nursing workforce. We document historical trends in skill level, average and relative wages, wage dispersion, unionization rates, and quantity, and find important divergences in the teaching and nursing professions that cannot be explained by previous theories. We posit two new theories that align with our documented trends: technological innovation and occupational differentiation in nursing. We argue that trends in the nursing profession indicate that declines in teaching quality were (and are) not inevitable.