FYI, never call your child stupid in front of him/her. I will never do that to my child. Do you know that by doing so you can actually cause a lot of damage? The child will think his parents think he's stupid. His confidence will be damaged.
Who in their right minds call their child stupid? Like I said, I will never, under any circumstances, say that to my child. Ever. What a bad example I'll be setting to my kid.
That's why some parents need to go for some parenting classes to actually learn what to say in front of their children. No matter how old the child is, he should never hear his parents calling him stupid. That's really degrading and wrong.