The association, which has published a leaflet for schools in an attempt to raise awareness of the problem, points out that while some pupils may be identifiable by frequent absences, others will strive to complete school work to avoid being identified as odd by their peer group.
Many worry that if they complain or ask for help the family will be split up and they will be taken into care. Disabled parents harbour the same fears, the association says.
The leaflet cites the case of a 12-year-old-girl who told classmates she went home to feed the dog at lunchtimes because she did not want them to know her mother had multiple sclerosis.
Teachers' main role is to give children an opportunity to talk about their situation without fear of the consequences and direct them towards appropriate agencies.
The leaflet also offers practical suggestions such as making sure pupils can make private telephone calls home to check on their relative. This can also make taking a day off school unnecessary.
Sylvia Heal, young carers' officer at the association, said there were no official statistics on the number of school-age carers, either from the Department of Health or local health authorities. What is clear is that support is often woefully inadequate. A survey last summer of more than 600 young carers found that a quarter were not receiving any help at all.
Sylvia Heal said: "One young university student used to write essays at school describing her family situation, in which she was the sole carer of her mother. She got As and B-plusses, but no teacher ever questioned her about the content. They assumed it was fiction."