Schools are too frequently having to exclude pupils to ensure they benefit from special support such as therapy or counselling, a report has said.
The study by The Inclusion Trust and the think tank LKMco called for more support for schools to keep children in mainstream education.
Only 1% of those receiving alternative provision go on to achieve five good GCSEs.
The government said schools had more power to act without excluding pupils.
Pupils who "sit on the margins of mainstream schools" are the focus of the report, which says they are entitled to a high-quality education that meets their needs.
Where children faced mental health issues or had involvement with social services, the right sort of support could often only be forthcoming once the pupil had been excluded, either for a fixed term or permanently, said lead author Loic Menzies.
This sort of drastic action was needed to encourage local authorities to take notice, he suggested.
The report also found there was a view that schools might not always be best placed to provide the support some young people required.
"This is particularly the case for those requiring skilled therapeutic interventions, but it may apply to other young people where different forms of engagement, a different set of activities or more intensive forms of support may be needed to address the challenges a young person faces.
"For this reason, some feel that trying to keep all young people in the mainstream is counter-productive, because exclusion brings access to additional interventions and funding.
"On the other hand, this raises the question of why it takes exclusion to trigger extra support," it added.
A Department for Education spokesman said: "Every child deserves the opportunity to develop the knowledge, skills and values to prepare them for life in modern Britain.
"That is why we have given schools more power to send pupils to alternative provision without excluding them first - and stop them from disrupting classes.
"We have taken action to raise standards for children in alternative provision by setting a clear expectation that they should receive an education on a par with mainstream schools."