It actually does work, but it is far more complicated than doing therapy exercises and requires extreme introspection and self awareness, more than it does a routine. The most effective way that I found that works, is internalization. Similar to how you learn to lucid dream over the years, you can use the same techniques to change your thinking patterns and "internalize" positivity. If it doesn't work, it is because the person themselves deny/reject that way of thinking/positivity. Exercises are meaningless, unless you actually see the value in them. You cannot go into the exercises thinking it will help you just by diligently doing what you are told. You need to understand the concept behind them. Coincidentally, people try to learn lucid dreaming and fail the same exact way. These repetitive exercises... end up failing at learning to lucid dream.
For example, you want to stop calling yourself stupid. You cannot just keep reminding yourself that you are smart, you are smart, you are smart etc. How do you internalize the idea of being smart? You must try to have faith in yourself. You become what you think. So when you find yourself doubting yourself, when you find yourself being made fun of, when you find yourself struggling with an intellectual problem. You simply change your thoughts from something like "I am stupid" to something like "I will get it eventually. I will figure it out. I will be able to do something about this." This type of thinking is building potentialin your thought process. Your brain will wire itself around improvement, and not be static black(negative) or white(positive). Your mind builds up walls and cages for its thoughts. You are the jailer, and the prisoner. To internalize positivity, is to internalize the potential to change yourself, simply by thinking you are capable of change.