"The Yutian middle school is a private school not covered by government funding, and it would not survive if it didn't achieve higher college enrollment rates than other schools," Liu said. "As a result, we see the vacation lessons as an extreme measure in pursuit of high exam grades."

However, the time spent on classes does not necessarily result in better exam results, said Liu Changming, principal of the Beijing No 4 High School.

"High grades come from students' better understanding of the material, and are not down to how many times a teacher repeats something in class. The students should be given enough time to digest the knowledge they learn at school."

Liu said his school had never given extra vacation classes.

"We certainly can work on improving our efficiency in class, instead of extending the teaching time," Liu added.

Jiang Chunyang, a researcher at the education college of Shenyang Normal University, blamed the teaching evaluation system. Jiang suggested that schools evaluate teacher performance based on the quality of their lessons instead of students' scores, and to take other factors, such as students' social activities, into account.

【Classes held undercover to beat study ban】相关文章：

★ Maldives president calls for unity govt

★ Pakistan condemns leak on Taliban aid

★ Millions of wives wed to gay men: expert

★ Europe freeze kills 89, fears rise over Russian gas supplies

★ China supports AL framework for solving Syria crisis: FM

★ Republican Romney sails to easy win in Nevada ballot

★ Italians turn to Web to battle tax evasion

★ Well-behaved prisoners allowed to celebrate festival at home

★ The unseen power of love

★ Hawking says 'look up at stars'