How do you stop echolalia. my child has pdd & is very sad to hear him repeat everything?

It is not easy: Behavior modification using rewards can help extinguish behavior. A strategy to substitute an acceptable behavior may work. Physical reminders, like wearing a rubber band on the wrist and snapping it when repetition starts can serve as a reminder to stop. Learning to mouth words rather than speaking them may be a step. Consult an autism behavior specialist to design an individualized plan.