Think of an apple tree. The behavior is the apples (the fruit). The heart is like the roots. If my apple tree is producing bad fruit can I fix it by going down to Whole Foods and buying some lovely organic apples and duct-taping them to the branches? Yet that is what we often try to do with our children. We teach them the right actions and then practically force them (as much as possible) to do them...duct-taping good apples on their tree while ignoring the real problems. We see that lovely fruit and think we have succeeded in parenting. Now if my apple tree has bad fruit, I may have to buy my apples (teach them the right actions), but meanwhile I need to find out what my apple tree needs to produce better fruit next year. Maybe I need to fertilize it or water it more or figure out some organic pest control or even prune it. I need to deal with the roots and the whole tree, NOT specifically with the fruit, for long-term fruit production. And this doesn't happen just once. It is an ongoing process...a long, long, process. It takes TIME, but eventually the fruit will grow on its own. Incidentally, this process does not just apply to our children, but to ourselves as well. My good friend Shannon posted a great post about this a few months ago. I'd highly recommend reading it.
There are so many scriptures about this (I've found almost 60 different passages so far!) I will write down a couple here (copied and pasted from Bible Gateway) and give you a list to look up yourself.
1 Samuel 16:7 (ESV)
But the LORD said to Samuel, "Do not look on his appearance or on the height of his stature, because I have rejected him. For the LORD sees not as man sees: man looks on the outward appearance, but the LORD looks on the heart."
Luke 16:15 (ESV)
And he said to them, "You are those who justify yourselves before men, but God knows your hearts. For what is exalted among men is an abomination in the sight of God.
Prov.1:7 and Prov. 9:10 (these verses go together in my opinion)
1 Cor. 4:5
2 Cor. 5:11-12
I would encourage you to open your Bible, or make use of Bible Gateway, or Blue Letter Bible (which included a concordance and links to commentaries and other study aids) and look some of these up. Be like the Bereans in Acts 17:11 who searched the scriptures for themselves to make sure that what they were taught was true.