Alexander, 12, Monika, 14, and Lisa, 15, had been receiving lessons from teachers at their former school in Amstetten, Austria, during the family's stay in a clinic since their father's incestuous crime was discovered in May.
The school's headmistress, Maria Hosa, has said the children "loved learning", and Fritz Lengauer, head of hospital security, said they were "looking forward to going back to school and meeting their new classmates".
"We wanted a harmonic start in the new school year," he said.
"Elisabeth is asking the media to leave them alone or we'll end the whole thing."
Josef Fritzl committed incest and locked up members of his family in a dungeon for 24 years. He will face up to 3,000 rape charges when he goes to trial.
Last week, senior legal sources revealed that Fritzl had admitted to sleeping with his daughter "two or three times a week" during her years locked in a basement prison.
Fritzl fathered seven children with 42-year-old Elisabeth, one of which died soon after birth.
The trial will be heard in private and could begin as early as December. Under Austrian law there must be eight jurors and two substitutes.
Source from Telegraph.co.uk