Pupils at six secondary schools in England are to be shown swearing, fighting and downloading porn in a documentary filmed with hidden cameras.
The teacher, known as Sylvia, first taught in the 1970s
They were filmed by a teacher using cameras in a button and a briefcase.
The NUT condemned the channel Five programme, due to be screened on Wednesday, saying it was not fair on the children to film them secretly.
Classroom Chaos does not identify any individuals, but its makers said it covered an "important national story".
The woman responsible for the filming, who is in her late 50s and had returned to supply teaching after a 30-year gap, is being identified only as "Sylvia Thomas", the pseudonym she used.
Over a period of about six months, she went into 18 schools in London and the north of England as a supply teacher and secretly filmed in six of them.
She says she saw chairs being smashed, pupils fighting in class and that she was sworn at by pupils and was falsely accused of touching them.
Other bad behaviour by pupils included verbal abuse, general rowdiness and the use of mobile phones or CD players.
Teaching sometimes became impossible, she said.
Five's senior programme controller, Chris Shaw, said: "I hope this film will open every parent's eyes to the chaos that reigns in many classrooms and makes meaningful teaching almost impossible."
The programme does not identify the individual schools, pupils or teachers involved.
The executive in charge of the production, documentary-maker Roger Graef, from Films of Record, said: "We decided very deliberately not to single out any one individual or school for particular criticism.
"We were not out to scapegoat but to reveal what happens behind closed doors. Teachers are the only ones who know what goes on.
"It is an important national story. There's a general collapse of respect for teachers and authority. Kids are controlling the corridors."
The National Union of Teachers condemned the programme, saying it was not right to film children secretly.
General secretary Steve Sinnott said: "Low-level disruption is a significant problem in our schools.
"We do not need underhand methods for a cheap documentary to expose the problem."
The union said the programme's methods were unacceptable and would not improve children's behaviour.
Mr Graef said the decision to go undercover was never taken lightly and that such filming was the only way to find out what was really happening in classrooms.
Classroom Chaos will be broadcast on Five on Wednesday 27 April at 2000 BST.