Thousands of "pinball kids" are bouncing around the care system putting their education and personal development at risk, the Children's Commissioner for England has warned.
Anne Longfield launched a new report on stability in social care that said 2,000 children had a change of care placement, school and social worker in a single year.
One in ten children in care experienced multiple changes in their care placement in 12 months, over 7,000 in total, often requiring a change of school.
A quarter experienced two or more changes in their social worker - nearly 18,000 youngsters.
As well as being damaging to their performance at school, the upheaval experienced by many children in care risks exacerbating behavioural and emotional difficulties, researchers warn.
The setbacks can make it more difficult for children to establish relationships, which in turn can lead to placements breaking down and a deeper sense of isolation.
Ms Longfield said: "Children in the care system crave stability, just like any other child.
"Especially for these kids, having reliable, consistent adults in their lives is critical to helping them flourish and overcome problems they may have experienced in the past.
"Sometimes changes are unavoidable and occur for the right reasons. But when 'pinball kids' are pinged around the system, it can damage them and their future prospects.
"Many of these children enter care with complex issues and are highly vulnerable. We must find a better, more consistent way of meeting their needs."
Around 50,000 children in care, 71%, experienced some type of change - placement, school or social worker - during the period analysed between 2015 and 2016.
One in 10 moved school in the middle of the academic year, three times the national rate.
Changing placement increases the chances of having to move school, however in just over half of cases children changed school without moving placement.
Ms Longford heard that one girl had not been to school for two years because she was in and out of care, while another was told she would be changing schools in the middle of her GCSEs by text.
The report has introduced a Stability Index, a new measure of continuity in children's care to help authorities track progress in reducing unnecessary changes and or unplanned moves.