Student–teacher ratio or student–faculty ratio is the number of students who attend a school or university divided by the number of teachers in the institution. For example, a student–teacher ratio of 10:1 indicates that there are 10 students for every one teacher. The term can also be reversed to create a teacher–student ratio. The ratio is often used as a proxy for class size, although various factors can lead to class size varying independently of student–teacher ratio (and vice versa). In most cases, the student–teacher ratio will be significantly lower than the average class size. Student–teacher ratios vary widely among developed countries. In primary education, the average student–teacher ratio among members of the Organisation for Economic Co-operation and Development (OECD) is just below 16, but ranges from 40 in Brazil to 28 in Mexico to 11 in Hungary and Luxembourg. Relationship to class size Factors that can affect the relationship between student–teacher ratio and class size include the number of teachers with non-teaching duties, the number of classes per teacher, and the number of teachers per class. In addition, if there are small classes for a small number of students, for example for special education or second language learners, the student–teacher ratio for the institution will be misleadingly low relative to the average student's experience. An example of this variation is that both Palestine and the United States have an average student–faculty ratio of 15, but the average class size is 21 in the United States but 27 in Palestine. Background A low student–teacher ratio is often used as a selling point to those choosing schools for tertiary education. On the other hand, high student–teacher ratio is often cited for criticizing proportionately underfunded schools or school systems, or as evidence of the need for legislative change or more funding for education. In the United States, some states have enacted legislation mandating a maximum student–teacher ratio for specific grade levels, particularly kindergarten. When such figures are stated for schools, they often represent averages (means) and thus are vulnerable to skewing. For example, figures may be biased as follows: if one classroom has a 30:1 ratio and another has a 10:1 ratio, the school could thus claim to have a 20:1 ratio overall. In schools, such ratios are indicative of possible staff changes. If the student–teacher ratio is 50:1, the school will probably consider hiring a few teachers. If the ratio is