Have you taken your son to the doctors? I just jumped on this site today and saw your post.
He drinks a lot. This is why I started checking him. My Grandfather was diagnosed with diabetes at 17 and died at 65 so this has me a bit scared.
prediabetic range is 101-125 fasting and I believe 140-150 post prandial. Do you have a history in your family, child drink excessively or urinate frequently at night? Is there a reason you are checking blood sugars? Need to call pediatrician and might have an A1C test done.