AFAIK it is the day they turn 18, if the child is still at school then the parent can request for the payments to be continued till the child is finished school.

There are other things in place, with regards to the earn/learn thingie (yeh great technical terms today!), in that if the child is deemed independent then the CSA payments are reduced, or if the child leaves home, the CSA payments go to the child, not to the other parent anymore.

S