Some children need a lot more repeating experience in order to keep the principle deep in their heart. Like my son, I just need to talk to him once or twice, he will not commit the said wrong doing again. For my girl, when compare with his brother of the same age, I need to spend at least 5 or 6 times of effort, i.e. repeat the "punishment" for at least 5 or 6 or even more time in order to let her understand what is wrong doing.
So, never give up! Insist and consistent are the most important of all!