in class we always had to.swap with the kid next to us and mark the homework- putting the right answer for those done wrong.

This child needs help. from parents and teacher. how long since a teacher looked at her books? least twice a week a teacher can go through the class and look at books. math especially has time for this.

I think here is a good example of falling through the cracks.

I think the question now is what should the op do?
talk to the parent? talk to the child? both?
I think the wording and approach will need to be thought out carefully here if any involvement on the ops behalf is to be of help. many parents don't want yo be told they aren't involved enough with their child.