As a clock in the sitting room ticked, the unhappiness on the face of 11-year-old Xu Xiangyu became increasingly evident. It was Saturday afternoon. The "darkest moment" was coming.

At 6:00 PM, Xu was sitting with a dozen children of his age in a classroom down in a narrow lane in urban Beijing. He was given a list of 16 mathematics questions. In one hour, he was supposed to solve them.

Apparently, Xu didn't. In the following hour, he sat silently, nonchalantly listening to an enthusiastic teacher lecturing about the answers to the mysterious math questions. Now and then, he could feel his mother's watchful eyes glancing at him from several rows behind.

His mother was taking notes. So were other parents and grandparents, who were listening to the lecture with their children.

"Those questions are so difficult that even I don't know the answers," said Xu's mother Huang Yan, who has a master's degree in communication. "I took notes in case he needs my help," said Huang.

The class Xu was attending, "Olympics math class," focused on math that was far above the level of primary school. Such after-school classes, along with others focusing either on English or Chinese literacy, are widespread across China.

To fifth-grader Xu, the math class (36 hours in total), which cost his mother more than 1,600 yuan (about US$235), was a "personal torture" besides a waste of time and money.

"What's the point of learning things that are useless in daily life?" said Xu, who spent one year in a London primary school from 2007 to 2008 when his mother studied there.

"For example, a question is like what's the sum of the first 500 figures of 1,2,3,2,3,4,3,4,5,4,5,6 ... Do you think the question means anything in life?" he said. "The class is like poison to me. I hate it."

But Xu's mother did not agree. "Almost all the kids in his class are attending such classes," she said. "I am afraid he would lag behind if he didn't. The competition for a good middle school is so intense."

To sixth-grader Zhao Zihao, in Xinxiang, a city 600 kilometers south of Beijing, a two-hour "Olympic math" class every week was nothing to complain about.

Zhao takes the class every Monday and Tuesday night and a two-hour after-school English class every Thursday and Friday night.

"I know he is tired. But what else can we do? We are from an ordinary family. He has to study hard to enter a good middle school," said his father Zhao Qingyong.

China's nine-year compulsory education covers primary and secondary school. No entrance tests are required for the students to enter public primary and secondary schools. Students are assigned to schools with reference to their residency, according to China's Law on Compulsory Education.

But in reality, a student can enroll in another school, usually a good one, rather than the one he or she is assigned to, if the student excels at math or English or has some special music or sports talent. A top award in "Olympic math" or English or a national certificate for piano performance will be a steppingstone to top secondary schools.

Other ways in are family connections with authorities or huge "voluntary donations" to a school.

The amount of the "donation" varies with schools. Zhao Qingyong said his son did not do well in a test organized by an agency, which he said represented the school he hoped his son could enter.

"I paid 50 yuan to the agency for the test. The agency said the top 120 students could enter the school without paying donations," he said. The school has 20 classes each grade and each class has about 50 students.

"I heard that the donation for that school is about 18,000 yuan," or about a year's saving for his family. "We need to find some guanxi (connections), otherwise we won't even have the chance to give the money," he said.