The research, released yesterday (23 October), is part of the What Makes The Difference project, which is examining ways to improve poor outcomes for looked-after children and careleavers.
The study found young people with the most care placements were two and a half times more likely to report a negative effect on their education and not be in education, employment or training. They were also three times as likely to spend time in prison than those with the lowest number of placements.
Project manager John Hill said: "There is already a vast amount of information from professionals and academics telling us what does and doesn't work - we wanted to let young people have their say."
Specially trained young people who had experience of care interviewed 265 young people from 25 local authorities.