A supply teacher who secretly filmed colleagues claims a school hid problem pupils during an inspection.
She says she was told by a classroom assistant how more than 20 of the most troublesome pupils were sent on a day trip.
She also claims the school drafted in full-time staff from other schools and senior staff taught classes they would not normally teach.
Alex Dolan, a qualified science teacher, worked in eight schools in Leeds and eight in London for six months during the investigation for Channel 4's Dispatches.
Footage from four schools, two from each city, filmed by a camera which she concealed on her, will be shown in Undercover Teacher, broadcast next Thursday at 9pm.
The film also claims to show pupils' widespread anti-social behaviour and disregard for teachers' authority.
The programme has reignited controversy over using hidden cameras to film in schools.
Leeds education authority is threatening legal action while unions say the film, which obscures faces but not voices of staff and pupils, is a breach of trust and infringes privacy. Other critics say it appears to misunderstand normal school practices.
A Channel 4 spokesman said the programme exposed "some shockingly bad behaviour" and "the apparent failure of the inspection system".
An Ofsted spokeswoman acknowledged the problem of schools "hiding" pupils but said that inspections were not compromised.
news 4, Leader 26