I'm Lucy, and I'd be happy to answer your questions today.
What Texas law says is that child support continues until the child turns 18 or graduates from high school, whichever is later. Family Code, Section 154.001. Check your court order to see if there is any differing language. If your son did not pass a high school equivalency exam before turning 18, is still living with the other parent, and is now in high school, yes, she could go back to court and get an order that you are required to keep paying support. The judge can modify your order.
You could try defeating such a motion by presenting evidence that your child told you they were never going to complete high school, if you reasonably relied upon that order, but you'll most likely have to keep paying until he drops out again, gets married, enlists in the military, or moves out of his mother's home.
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