This study seems a little superficial to me. It is like the issue of self-esteem. Of course, success is more likely when she has confidence in her abilities. The problem is success breeds confidence and visa versa. It does no good to demand more confidence. Flattery and gushing praise is not helpful either. Confidence has to be earned. Start small and work at it. The study did mention that everyone put in extra time, not just the student or the teacher.