A "D" is a "D"

Well correct me if I'm wrong but when I was in high school when you got a "D" it was a "D" no matter what percentage it was at?  My son Austin has a "D" in reading and insist that because it is a high "D" he should not be grounded?  So is a 68% still a "D"?  YES IT IS!  Sorry Austin but your still grounded.  Now I'm not sure who is really being punished me or him?  It seems that whenever my boys are grounded they hang around me all the time.  I know their game.  Lets bug mom till she let's us off being grounded so she can have peace and quiet.  Again, sorry boys but I'm on to you!  Bug away because it just makes me more angry and I'll start taking away more!  Not that I don't love being with my boys; I love them with everything I have.  I don't have much but what I do have is theirs.  As, I sit hear and type my daily woes I'm listening to them argue about names??  Well, I guess Harvard is out.  Maybe Hillsborough Community College would take them?