With no extra money for more teachers, staff are finding the classes unmanageable.
The phenomenon of massive class sizes began in cities in the early 1990s as the easing of rules for registering city residents led to the population of China becoming more mobile. Many Chinese people have moved from villages to towns in search of jobs. This has increased the pressure on city schools.
In Beijing, which has an official population of 10 million, more than 1 million have registered as temporary residents but it is believed twice that number could be flooding into the capital. Over the past five years some 90 million people are thought to have moved from rural areas to the towns.
The floating population also manages to evade the strict rules limiting families to only one child, so migrants often have more than one child to educate.
One headteacher in Shunde, in the southern province of Guangdong, noted that schools on the outskirts of towns were particularly badly hit because parents prefer to send their children to city schools where the standard of education is considered to be much higher than in the severely underfunded village schools.
Ironically, while bemoaning the size of classes in state schools, the authorities are calling on expensive private schools to increase class sizes as a way of reducing the burden of their high fees on individual families. Private schools have been tolerated because they were thought to help reduce the overload on the state sector.
However, because very few are being educated in such schools they are having almost no effect on growing class sizes in the state sector. Class sizes of 18 to 30 in private schools serve merely to highlight the crisis in city classrooms and attract frazzled teachers away from the state sector.
Meanwhile, during the March session of the National People's Congress, China's parliament, delegates rejected a bid to increase government spending on education from the current 2.6 per cent of gross domestic product to about the 4 per cent other developing countries spend. It is expected to fall to 2 per cent of GDP this year.
The requirement that 20 per cent of local government expenditure should go towards education was also dropped from the education law, which has taken 10 years to draft. This prompted criticism that the new law fails to provide guarantees for funding which is often insufficient or misused. In some provinces, payment of teachers salaries is often delayed for months because of shortages of funds.