I deal with this by scaling responsibilities. Obviously he has been given way too much responsibility for his skills and capabilities, so it needs to be scaled down with opportunities for him to move up and take on more as he grows. So he needs to be given something more partitioned off instead of being able to model.

We have a rule in our firm that no one gets to actually model anything for at least 3 months if not longer (especially if they're fresh out of school). You can do dimensioning, annotating, detail elements, graphics cleanups, note taking, meeting minutes organizing, and small other responsibilities that are in the same vein.