Decreasing class sizes, even by as little as one student, comes with a price tag. It is possible to “pay” for this increase by compensating with one of the other factors influencing the salary cost of teachers: lower teachers’ salaries, less required instruction time for students or more teaching time for teachers. Across OECD countries there seems to be a trade-off between smaller class sizes and higher teachers’ salaries, thus prompting the question of which policy leads to the best student outcomes. The evidence points to the importance of ensuring high-quality teaching above all else. Although higher salaries can help achieve that, several other factors will also influence the quality of the teaching force and of the country’s educational system as whole.