RIYADH (Reuters) – Some countries fret over the number of teenagers skipping school, but Saudi Arabia is worried about truancy of another kind — teachers playing hooky to trade on the booming stock market in the world’s top oil producer.

Saudi Arabia’s education ministry said Thursday it had told headmasters to ensure that teachers do not use work hours for the national pastime of dabbling in the Arab world’s largest stock market.

“There have been some cases, concentrated in Riyadh and Jeddah … over the last year when the stock market has seen a lot of activity,” a spokesman said. “There are natural reasons for having to leave school and unnatural ones, such as trading in shares.”

Record oil receipts helped the Saudi bourse rise by 104 percent last year. Analysts say half the country’s 18 million citizens are believed to hold shares in listed companies, and some 3 million trade regularly.