International schools in Japan are classified as "miscellaneous schools" under the School Education Law, which means they are not accredited domestically.

Consequently, the government does not differentiate between international schools and cooking, sewing or driving schools -- although international schools are accredited overseas.

Graduates from international schools are thus unable to take entrance exams for Japanese high schools until they obtain an equivalency certificate for lower secondary school, which requires passing a separate exam.

Similarly for graduates wanting to enter Japanese universities; they must first pass "daiken" exams that qualify them to take university entrance exams.

Only a few private high schools and universities are exempt from this requirement. But some observers say many international school students never intend to enroll in Japanese colleges.

"Many of our alumni go abroad and graduate from universities abroad and end up living abroad," said Thomas Walters, headmaster of Nishimachi International School in Tokyo.

"This is a bit of a brain drain for Japan."

The legal status of the schools also affects their finances.

The only subsidies they receive are small and come from local governments, while any donations they receive are not tax deductible.

As a result, the schools charge high tuition fees -- around 2 million yen a year -- for facilities that are poor compared with local Japanese schools.

"Japan should foster international schools and see us as a great resource for its future," Walters said, adding that the high tuition fees exclude a lot of families.

Pundits also point out the inconsistency between allowing Japanese educated abroad to take university entrance exams while banning international school students from doing so.

The education ministry, however, is reluctant to take action to upgrade the status of international schools.

Most countries have a national exam used to evaluate aptitude before entering college.

As Japan does not have a national exam, instead relying on universities to screen students who have completed high school education, the ministry said there is no guarantee that international students have obtained the minimum standard of education required in Japanese schools. Hence the daiken, which was originally designed for Japanese students who fail to complete high school.

The survey also shows that most countries and regions do not provide subsidies to international schools.

"When looking from the opposite point of view, international schools enjoy the academic freedom to choose their own curricula," said Hiroaki Motomura, the unit chief of the ministry's international affairs division.

"If the state provided international schools with a status similar to mainstream schools, we would have to intervene in their curricula."