Students who have not left pupil referral units (PRUs) by the end of Year 9 should not return to mainstream schools, according to the head of a leading PRU.
Instead, they should remain in their units until they have taken their GCSEs, says John d'Abbro, head of The New Rush Hall Group in Essex.
Speaking at the National Children and Adult Services conference in Manchester last week, Mr d'Abbro said: "If a student is not back in a mainstream school by the back end of Year 9, it is often better that they don't go back.
"If you keep them on in the PRU, you can then hothouse them in preparation for their GCSEs. We had one boy where this was applied and he took 10 GCSEs and gained nine A*s."
Mr d'Abbro's views contradict Government guidance, which calls for pupils to be returned to the mainstream as soon as possible.
Mr d'Abbro added that the issue will become more pressing once the compulsory participation age of pupils is raised.
The hothouse practice is backed by Stuart Bailey, head of Parkside PRU in Ipswich, which specialises in children at key stage 4.
"It is a system that we wholly endorse, and one we try to implement," Mr Bailey said. "It can take us three, four, five months to get our pupils back into the routine of learning, coming into school and engaging with teachers again.
"If you are dealing with pupils who have mental health issues - such as our school, where 60 per cent of the kids have attention deficit disorder - it is easier for them to take time out in a PRU. It is very difficult to do that at a mainstream school."