What is the ruling on differential treatment among children, especially when their academic levels vary? And is it Islamically permissible to change the treatment of a daughter who has failed in order to motivate her to succeed, or should another method be followed?

A father must be just among his children. However, he may favor some of them with something for a valid reason. If his harsh treatment of one of his daughters is due to a specific need or circumstances, there is no harm in it. A father is not required to treat all his children—the good and the bad—equally, while cautioning against destructive negative criticism and advising gentleness.