The public education system in Egypt consists of three levels: the basic education stage for 4–14 years old: kindergarten for two years followed by primary school for six years and preparatory school (ISCED Level 2) for three years. Then, the secondary school (ISCED Level 3) stage is for three years, for ages 15 to 17, followed by the tertiary level. Education is made compulsory for 9 academic years between the ages of 4 and 14. Moreover, all levels of education are free within any government-run schools. According to the World Bank, there are great differences in the educational attainment of the rich and the poor, also known as the "wealth gap." Although the median years of school completed by the rich and the poor is only one or two years but the wealth gap reaches as high as nine or ten years. In the case of Egypt, the wealth gap was a modest 3 years in the mid-1990s.