The school year extends from September 1 to end of May and is divided into four terms. Study programme in schools is fixed; unlike in some Western countries, schoolchildren or their parents have no choice of study subjects. Class load per student (638 hours a year for nine-year-olds, 893 for thirteen-year-olds) is lower than in Chile, Peru or Thailand, and slightly lower that in most states of the United States, although official hours are frequently appended with additional classwork. Students are graded on a 5-step scale, ranging in practice from 2 ("unacceptable") to 5 ("excellent"); 1 is a rarely used sign of extreme failure. Teachers regularly subdivide these grades (i.e. 4+, 5−) in daily use, but term and year results are graded strictly 2, 3, 4 or 5.