A report claims that some schools in England are illegally excluding pupils without going through the formal expulsion process.
England's children's commissioner Dr Maggie Atkinson was told that some students were moved on to other schools or sent home without their exclusion being properly recorded.
She said that most schools tried to work with their more troubled youngsters, but some expelled children 'on a whim'.
The report, They Never Give Up on You, reveals that 2.5 of school population are permanently excluded yearly.
It also states that those children with special needs were most likely to be excluded, and that Black Caribbean pupils were four times more likely to be expelled.
The BBC reported that 'one extreme example' concerned a school head who told researchers he was planning on sending a group of final-year GCSE pupils home from Christmas until May.
He reportedly told the researchers: "We will get their parents in and ask them to keep their children at home for the rest of the academic year; otherwise it's permanent exclusion.
"The pupils are coded as 'C' (authorised absence) and slip under the radar."
The report says that the practice is 'illegal and simply unacceptable' but admits that it is 'extremely hard to identify and quantify' because the expulsions are 'covert and informal with no records kept.'
It notes that DfE guidance on 'formal exclusion' is 'clear and unequivocal' and is the only legal method of removing a child from school, whether for part of a day or longer.
It also acknowledged that many parents do not complain about their children being removed because they are unaware of the legislation and their rights.
Dr Atkinson said: "We knew a minority of schools excluded informally and therefore illegally, but for the first time in this inquiry we have this on record.
"Whilst most schools work far beyond the call of duty to hold on to troubled and vulnerable children, a minority exclude on what seems to the observer to be a whim."
The report says it accepts there is a need for pupils to be excluded from time to time, but warns expulsion should only happen when they are harming themselves or others, or if they are preventing others from learning.
Do you have experience of this? Do schools expel children too readily?