Elementary school is mandatory for children ages 6–14. There are nine "years" (as opposed to the former eight "grades"). The current "first year" broadly corresponds to the former pre-school last year of private institutions, and its aim is to achieve literacy. Generally speaking, the only prerequisite for enrolling in first year is that a child should be 6 years old, but some education systems allow children younger than 6 to enroll in first year (as long as they turn 6 during the first academic semester). Older students who have not completed their elementary education are allowed to attend, though those over 18 are separated from the younger children.