A mother’s fight to find out why her daughter was not admitted to one of Thailand’s leading primaries has set a legal precedent that threatens to expose major corruption in the entrance procedures of top state schools.

Parents have paid up to 10 million baht (pound;167,000) to secure places at one school, according to research at Bangkok’s Chulalongkorn University.

Sumalee Limpa-ovart has become the first parent to demand the disclosure of exam results under a new official information Act. The legislation gives Thais the right to access to all state information that does not threaten “national security” or infringe personal privacy.

Her request to see the scores of the first-grade entrance tests to the Kasetsart university demonstration school in Bangkok prompted a swift legal response from more than 100 parents of pupils who did get in. However, they were rebutted by the civil court, which declared the exam results to be public information.

The legal wrangle highlights claims that top schools, particularly the centres of excellence run by the leading universities, routinely favour families who give donations.

Dr Sompong Jitradab, of Chulalongkorn University’s faculty of education, questioned parents of students at one such school and found that money, cars and equipment had been given through its parents’ association.

The investigation, which showed that many of the students came from prominent families, indicated that only 70 of the 123 admitted had qualified through high marks in the entrance exam.

Thai education officials admit such favouritism exists, but insist that it is very limited in its extent.

Pibhop Dhongchai, civil-rights campaigner and educationist, said he hoped the legislation would mark a sea change.

“There is a tradition of influential figures getting their kids into the top schools. With more transparency under the information act, this will no longer be acceptable,” he told The TES.

But Kasetsart University has balked at giving Mrs Sumalee straight answers, providing only lists of names and figures.

A Bangkok Post editorial promptly accused the school of “squirming to keep secret what everybody knows about”.