The ministry of education defines international schools as, "...an educational institution providing an international curriculum or international curriculum which its subject's detail has been adjusted or a self-organised curriculum, which is not the Ministry of Education's. A foreign language is used as the medium of teaching and learning and students are enrolled without restriction or limitation on nationality or religion or government regime, and are not against the morality or stability of Thailand."
Prior to 1992, only a very small number of international schools existed in Thailand, and they catered entirely to the children of expatriates, as Thai law prohibited Thai nationals from enrolling. When the first international school, International School Bangkok, relocated to a new campus outside of the city proper, a group of parents worked with United Nations staff to lobby the Ministry of Education to change this law and open the first new international school in decades. This led to the establishment of New International School of Thailand (later changed to NIST International School), and the repeal of the prohibition against the enrollment of Thais. Due to the high demand for private international education, this change also sparked the opening of dozens of other international schools over the subsequent years.
The curriculum is required to be approved by the Ministry of Education and may be an international one, an international curriculum with modifications, or a curriculum established by the school itself. Thai language and culture constitutes a core subject and is mandatory at every level for all Thai students registered as Thai nationals. Non-Thai citizens are not required to study Thai language or culture. International schools must operate within a framework of requirements and conditions established by the Ministry of Education, that stipulates the ownership, location and size of the plot, design and structure of buildings, ratio of students to classroom surface, sanitary installations, administration and educational support facilities such as libraries and resources centres. Within one year from their commencement, elementary and secondary schools must apply accreditation from an international organisation recognised and accepted by the Office of the Private Education Commission and accreditation must be granted within six years. Managers and head teachers must be of Thai nationality though frequently there will also be a foreign head teacher to oversee the international curriculum and implement school policy.
Approximately 90 international schools operate in Thailand, of which about two-thirds are in the Bangkok area.