Police said Sunday that they had begun an investigation about an alleged disclosure of test questions at a girls’ high school in Seoul’s Gangnam district.

The Seoul Metropolitan Office of Education carried out a special inspection from Aug. 16 to 22 after a senior teacher at the school was suspected of divulging test questions to his twin daughters.

Suspicion grew when both students attained the top rank in the liberal arts and science categories for their grade this past semester. A year earlier, the students had ranked 59th and 121th, but jumped to second and fifth place after a semester and finally reached the top.

The twins came under suspicion of cheating, and it was discovered that the teacher in question had up to 50 minutes to check the test questions in advance without any other teachers present.

The education office requested a police investigation, saying an internal inspection was not enough.

“We are currently viewing the education office’s inspection data,” the Seoul Suseo Police said. “We plan to investigate the case promptly.”

By Kim Jee-min (jeeminkim@heraldcorp.com)