Some children staying in hospital are not getting as much of an education as those in England, a study has found.
Children's Commissioner Rocio Cifuentes said there were also "unequal experiences" for children across Wales and called for clearer guidance.
One teacher said a pupil asked to study for her maths GCSE on the day of her terminal cancer diagnosis.
The Welsh government said all children, regardless of their circumstances, had a right to a full education.
Isabel Thomas, a teacher at a children's hospital in Cardiff, said the girl, who went on to achieve several GCSEs, was "probably the bravest young person I've ever met".
She said learning maths "broke up the day for her. It gave her a sense of normality... which is what she was craving in a very traumatic time".
