Positive reinforcement vs negative reinforcement

If your child got a C+ on his test, what would you say to him?

What if he usually gets D minus? That's progress, right?

You can scold and scoff at them for getting poor grades.

or... 

You can say, "Well, this is an improvement. I am glad you worked hard to improve your grades. Is there anything I can do to help you further improve this?"

The first option, i.e. making them feel bad, may work. It might also have the side effect of them trying to avoid you. 

The second option works at least as well as the first option. It will also make them feel secure, reinforce their work ethic, and helps build a positive personality.

Going with the encouragement method may feel weird if you weren't talked to positively as a kid. But it's worth a shot.