Shopping trolleys, piles of concrete and bicycles are placed frequently on railway lines and stones are often thrown at carriages by pupils on overhead bridges, says the British Transport Police.
The latest craze is to remove bus windows and drop them on passers-by or fellow pupils, according to Cowie, London's biggest bus operator, which transports more than 20,000 pupils in the capital. The company says that pupils use etching tools to cut away the rubber seals which secure the windows.
The extent of the vandalism operators are facing has emerged following last week's decision by the West Anglia Northern Line to ban a school from its trains after pupils vandalised carriages and abused staff and passengers.
Pupils at Mount Grace School in Potters Bar, Hertfordshire, are now only allowed on Northern Line trains when accompanied by an adult. Other transport operators this week said they would not be banning pupils but revealed that they have been forced to think up new ways to curb vandalism.
Cowie admits pupils are costing the company more than Pounds 5 million a year in repairs. The company buys graffiti remover by the crate and in the past few months it has installed covert cameras to catch vandals. Instead of pressing charges, it forces the culprits to clean the buses at weekends.
"The standard of behaviour among schoolchildren is deteriorating," says a spokesman for Cowie. "Our staff are more likely to be attacked during school hours than late at night."
Rival bus and train operator Stagecoach says that travelling with schoolchildren is "a nightmare" for other passengers. In some areas the company has been forced to offer "X-rated services" - children are not allowed on unless accompanied by an adult.
"We do get more vandalism than before and we have noticed a general decline in behaviour," says a spokeswoman. "Schoolchildren are often found removing seat bases and using them to surf down the top deck of the bus or they hit each other while standing on the stairs."
The discipline problem is not confined to transport. Newsagents are also in the front line. Many shops now limit the number of children on their premises having suffered theft or abuse in the past.
"Children are cheekier than they used to be," says David Daniel of the National Federation of Retail Newsagents. "In the past if they behaved badly a policeman would sort them out with a clip round the ear, but if he did that now, he'd probably get lynched."
John Sutton, general secretary of the Secondary Heads Association, points out that parents are legally responsible for their children's behaviour unless they are in school or on an organised trip from school.
Mr Sutton blames parents for the decline in pupils' behaviour. He believes, however, that schools and parents have a joint responsibility to improve the situation.
In a bid to halt the danger caused by children throwing stones at trains, the British Transport Police has been taking drivers into schools to tell pupils how it feels when a stone hits the window of a train travelling at l00 miles an hour. The police admit they are desperate to act before children become totally out of control. A spokesman says: "If children's vandalism becomes a police problem, we have failed."