Teachers are the most important school resource. In every country, teachers’ salaries and training represent the greatest share of expenditure on education; and this investment in teachers can have significant returns. Research shows that being taught by the best teachers can make a real difference in the learning and life outcomes of otherwise similar students. But not all students are equal when it comes to access to high-quality teaching. In fact, PISA data show that there are inequities in access to experienced and qualified teachers in many countries, and that they are related to the gap in learning outcomes between advantaged and disadvantaged students.