What will or do you expect?
When it comes to grades, what do you expect? Do you expect honor roll and nothing less? Or are you just happy if they pass? Something in between?
My answer here depends on the child. I know my oldest has learning issues so I expect at least average from her, which is a C. In certain topics I expect higher because I know she is capable of it, like choir for example. She should never have less and an A, if she does it is because she wasn't putting forth effort.
With my son I do expect B's and above. I know he is more than capable of it. I don't get upset over a C, but I ask him why he had a C, if something was difficult for him. Then I go over whatever it is that was frustrating to him and that seems to help.