Students should no longer be excluded for "minor infringements" such as wearing jewellery or incorrect school uniform, according to a report by the Children's Commissioner for England.
Dr Maggie Atkinson said pupils should only face exclusion from their schools to protect the safety and learning.
The report also warned of "illegal practices" where schools send children home but the child's exit is not recorded as a formal exclusion.
John Connolly, Dr Atkinson's principal policy adviser for education, insisted that the advice on school uniform did not amount to condoning defiant behaviour by pupils.
"We are not saying don't have uniform, we are not saying don't have rules about personal appearance, what we are saying is don't remove education for those reasons," he said.
"By all means use detention or internal exclusion or take lunchtime off them... actually what we have found is that is more likely to change behaviour than repeated short-term exclusions any way.
"The test that we would set on this is that if you are not hurting yourself or anyone else and you are not stopping anyone else from learning, those should be the criteria for whether or not it is OK to exclude," he added.
"So the disruptive behaviour in class is stopping other people from learning - so the school is well within its rights to protect the learning of the other children in the class.
"But if it is about chewing gum, then that is different."
Dr Atkinson said current exclusion guidance stated that it was not appropriate to exclude a pupil on the basis of minor infringements such as wrong coloured shoes or too much make-up.
She said this had been removed from revised guidance which was issued just before Christmas for consultation.
The report showed that 5,740 children were permanently excluded from state-funded schools in 2009/10 and 179,800 young people excluded on a fixed-term basis at least once during that year.
The strongest predictor of being excluded from school, either permanently or on a fixed-term basis, was having special educational needs, followed by being black Caribbean, for permanent exclusion, or male, for fixed-term exclusions.
"Many schools do fantastic work to hold on to difficult and troubled children and to work with their families," Dr Atkinson said.
"What has not closed however are the gaps between who is and who is not excluded."
She added that her inquiry had uncovered "compelling evidence" of a number of illegal exclusions made by schools.
These included unrecorded short-term exclusions to allow children to "cool off", and students being sent home and not allowed back until after a meeting has taken place with their parents. Where parents were unwilling or unable to attend a meeting the illegal exclusion could last for a week or more.
Dr Atkinson said: "Excluding the child simply by saying 'You are not very happy here, are you? Why don't you not come back next Monday?' is unacceptable.
"It is irresponsible. Those working with children who are already vulnerable and may be living in very difficult and complicated and perhaps chaotic households would tell you that if you simply send a child home and you don't know what you are sending them to, you are in dereliction of your duty, and I would agree."
Connolly said he believed some heads sending children home without recording their absence as an exclusion thought they were acting in the best interests of the child while others may be unaware that they are breaking the law.
A Department for Education spokesman said: "Unless there is good behaviour in schools, teachers cannot teach and students cannot learn. Schools need to be able to exclude disruptive pupils as a last resort: to enforce non-negotiable school rules, to protect staff and students and to guarantee that excluded children get the support they need.
"Our policy on exclusions is the right one, and we will continue to support it. Obviously unofficial exclusions are unlawful. All schools must follow the legal exclusion process."
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said: "The coalition Government has been very clear about its commitment to giving headteachers the power to make whatever professional judgments are necessary in order to maintain high standards of discipline.
"Heads do not make decisions about exclusions lightly and are not allowed to delegate them. Each individual case needs to be considered and ASCL opposes the suggestion that new blanket restrictions should be put in place.
"Sometimes what superficially appear to be relatively minor breaches of school rules can be acts of defiance which, if not dealt with robustly, soon pave the way for a more widespread decline in behaviour.
"School leaders are well aware of those groups which are more likely to be permanently excluded. Complex, deep-seated social issues underlie this to which, sadly, there are no simple solutions.
"School leaders agree that we need to do everything we can through preventative strategies to build on current best practice to give young people from these groups access to the best possible education."
Gavin Poole, executive director of the think tank The Centre For Social Justice, said: "Yet another report is published that highlights the tragedy that faces too many vulnerable children.
"Schools must engage with the parents to address the underlying issues and parents must be compelled to engage when they refuse."
More:Dr Maggie Atkinson UK News The Centre For Social Justice Uk Students Uk Schools Brian Lightman
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