Child support applies until your child turns 18 years old. However the assessment may be extended in some circumstances.
If your child turns 18 while attending secondary school, you can ask CSA to extend the assessment until their last day of the school year in which they turn 18. To do this, you must apply when your child is 17 and prove that they will be in full-time secondary education on their 18th birthday.
If you have a court order that ends on the child's 18th birthday and that child will be dependent on you while completing their final year of secondary education, you will need to apply to the court if you want the order extended. Please read the court order to decide whether you need to do this. Alternatively you may determine a private arrangement with the other parent for the support of the child until such time as the child is able to support themselves.