Non-government schools can be further classified, based on self-identification of the school’s affiliation. Non-government schools are grouped for reporting as Catholic schools (including Catholic-affiliated independent schools) or independent (other non-government schools). Government schools receive funding from the relevant state or territory government. Non-government schools receive funding from the Australian Government and relevant state or territory government; and in most cases parents are required to make a co-payment for their child's education. A small portion of students are legally home-schooled, particularly in rural areas. Also sometimes called infants schools, Australia adopts the UNESCO term of primary school that generally covers a child's education from pre-Year 1) and finish with Year 6. The duration of primary school years vary across each Australian state and territory, with most adopting seven years; except in South Australia, where students finish with Year 7, making the duration of primary school eight years; until they are 11 or 12 years of age. Primary schools focus on developing essential literacy, numeracy and social skills, and provide foundational knowledge to children about the world around them. Also called high schools and colleges (or junior, intermediate, or senior colleges), secondary schools vary across each Australian state and territory, however generally cover from Year 7 to Year 10 (compulsory period of education) and beyond to Year 12. In the majority of Australian states and territories, middle schools are relatively uncommon. Students progress from primary school to secondary school. As an alternative to the middle school model, some secondary schools divided their grades into "junior high school" (Years 7, 8, 9 and 10) and "senior high school" (Years 11 and 12). Some have three levels, "junior" (Years 7 and 8), "intermediate" (Years 9 and 10), and "senior" (Years 11 and 12). In June 2006 the Northern Territory Government introduced a three tier system featuring middle schools for Year 7 to Year 9 (approximate age 13–15) and high school for Year 10 to Year 12 (approximate age 16–18). In Australia combined schools are schools that have classes from both primary and secondary year levels. These schools may be located in urban, regional or rural area and may be government or non-government schools. there were approximately 500 Australian combined government schools and approximately 850 Australian combined non-government schools. Central schools are predominately, but not exclusively, government schools located in a rural area that provides both primary and lower secondary education to students, usually concluding at Year 10. there were 62 Australian central schools, and all except one were located in rural New South Wales.