Local authorities have been advising headteachers to exclude troublesome pupils so that their school looks good in Ofsted inspections, research reveals.
Heads with disappointing test results have also been told to place pupils on the special needs register to escape criticism from inspectors.
The findings follow a three-year study of strategies for urban school improvement by academics at Manchester university.
They relate to one council, which has been praised for its work on school improvement. However, Professor Mel Ainscow, who led the research, said the phenomenon was widespread. "I've certainly met it in quite a few places, in one form or another," he said.
Chris Darlington, past president of the National Association of Special Educational Needs, said: "This is immoral."
The report said: "During the run-in to an inspection, (local authority) school improvement officers tended to want to help schools to present themselves in the most favourable way.
"For example, it might be suggested to a headteacher who had disappointing test results in relation to the school's targets that more children could be placed on the special needs register.
"This implied that greater progress could not be expected from these particular pupils."
A consultant working with the council told how some school improvement officers had "helped youngsters out of the window" in the run-up to an inspection, to make classes easier to manage.
He said the brief from council officials had been to get schools out of special measures quickly or to stop them failing.
But the consultant said: "(This) has resulted in children being excluded, sometimes in groups.
"It has also resulted in students being removed to special schools for a term, without a statement... They don't go back. Once they are out, they stay out.
"That is a long, long way removed from saying that your responsibility is to provide an education for all the children that are in your community."
The report concluded: "The apparently successful efforts of this particular local education authority to respond to the Government's demands for improved standards had, in practice, created barriers to the participation of certain groups of pupils."
Professor Ainscow said inspections and testing had helped to put pressure on many schools to improve.
Yet they also had introduced a degree of "corruption", in which schools were encouraged to take any measure available to demonstrate apparent improvements, even if these were anti-educational for some pupils.
An Ofsted spokeswoman said: "Incidents of pupils being removed from school prior to an inspection are rare, but Ofsted does not condone any attempt to give a false picture of a school's provision."
Since last year, schools had had only three days' warning of inspections, making it even more difficult for such abuses to occur, she said.