Vietnam's education system can be divided into 5 categories: pre-primary, primary, intermediate, secondary, and higher education. Public kindergartens usually admit children from the age of 18 months to 5 years. Children at 4 or 5 years of age are sometimes taught the alphabet and basic math. This level of education is only popular in major cities. Children normally start their primary education at the age of six. Education at this level lasts 5 years and it is compulsory for all children. This compulsory education may be one of the reasons why, despite remaining a less developed country, the literate proportion of the country's population is very high, over 90% on average. Middle schools teach students from grade 6 to 9. This educational level is generalized throughout most of the country - except in very remote provinces, which expect to popularize and standardize middle education fully within the next few years. Intermediate is a non-compulsory schooling form in Vietnam. Secondary education, which consists of grades 10, 11 and 12, is standardized in all major urban regions, but is not in rural provinces. After 3 high school terms, all students must attend a graduation test. This test often consists of 6 subjects differently selected each year but has to contain the 3 compulsory ones: Foreign Language (mostly English), Mathematics and Literature. The Vietnamese government intends to merge this test with the university entrance test in 2009.