Show him this video.
Sarah practicing serve.She is 8 years old. http://www.youtube.com/watch?v=-L7q-...eature=related
No way he'll let Sarah out serve him.
Separate out the pronation aspect of the serve by doing the following pronation exercise.
McCraw explaining a serve pronation exercise http://www.youtube.com/watch?v=iONY6fcqZGg
Starting on the service line, instead of the baseline, as Coach McCraw describes, takes the pressure out of trying to get the ball in, and instead allows him to concentrate on the motion.
Start with no more than 25 serves of this exercise so as not to cause undue arm soreness.
Make sure that when he drops the racquet it is well out to his right side - the "back scratch" position is not in the middle of the back but well out to the right [assuming he is right handed].
If you don't start with the racquet well out the right in the racquet drop, you can't rotate it right to left in the pronation movement (pics 10-20).
Pronation is not apparent to those learning to serve, and you as his teacher will have to make sure he is setting it up and executing it correctly. Standing in back of him may give you the best perspective.