Legal Question in Family Law in California

Not if the child is still a full time high school student. If they are, it continues until they leave high school or turn 19, whichever comes first. Under certain limited circumstances it can be extended, generally in situations with special needs kids.

Just to add, once the child turns 18 and graduates doesn't mean that a wage assignment will suddenly disappear. If you have a wage assignment, you may wish to speak to an attorney or the family law facilitator's office in your local county for how to obtain a termination of wage assignment/zero order.