A value of zero indicates that there is no difference between socio-economically advantaged and disadvantaged schools in how concerned principals are about the educational staff at school, and positive values (higher equity) indicate that principals' in socio-economically advantaged schools are more concerned than principals in disadvantaged schools. For example, schools with large special education programmes and more teaching assistants tend to have more teachers, but the schools' high student-teacher ratio has no impact on the size of regular classes. In addition, the amount of preparation time per day allotted to teachers may vary across schools and across school systems.