In other words, the causal direction of this association cannot be determined. However, in more than a third of countries and economies, including many that compensate for disadvantage in schools by allocating more teachers to those schools, teachers in the most disadvantaged schools are less qualified and/or experienced than those in the most advantaged schools (Figure 1.2). Sometimes, the very policies that channel more resources to high-need schools might, in fact, deter more-experienced teachers from teaching in these schools. Where centrally set rules for promotion and mobility of teachers privilege teacher preferences and give priority to more senior teachers, and where teachers' pay does not vary greatly across schools or across teachers with similar experience and qualifications, it appears difficult to avoid attracting a high concentration of the most experienced teachers in the most prestigious schools.