Dame Rachel, whose role exists to protect and promote the rights of children, said many families were turning to home education out of desperation, not choice.
"I think it’s shocking to see how many children have been home educated because I know so many of them are not doing it because they want to,” she said.
"I'm deeply, deeply concerned. I think this is forced home education."
She added it was often children with special educational needs, children in the poorest areas and children at risk of exclusion who were being taught at home.
"They're becoming electively home educated as a last resort,” said Dame Rachel. “They're not getting what they need in school. I don't think it is a positive choice for many young people.
“Many of these children are the lockdown generation who actually were at home and have found it difficult to get back."