How Praising Your Kids Might Backfire . . .
In a way this is a subtle point. But an important one. The accepted theory with reinforcement for children is to acknowledge the behaviour that you want more of.
When it comes to learning - praising a child's intelligence may seem like a good idea: “you’re very smart”. But since intelligence is mostly thought of as something one has or has not, such praise does not reinforce a behaviour. There is now some research to show that for some kids this kind of praise may backfire in that they may figure that if a problem seems too hard it is because they lack an innate ability which can't be fixed. Whereas by praising a behaviour “you really worked that one out” or “you worked at that really well”, they will learn to keep at a problem and thereby learn and develop.
I recognise this in myself, when I somehow expect to be able to “just do this” when it actually requires patience and learning. There is a temptation to give up instead of persevering.
There's a good summary here with references to original research.