Discrimination
"On the other hand, there is an imbalance in Education. Most teachers are women, especially in primary schools. Should a sensitive principal hire more men?"
They should, but somehow these worries about gender imbalance and the need to include more of the opposite gender in a field or workplace only appear when the ratio is more men than women.
I have never seen anyone making programs or quotas to insure that more men enter into preschool teaching or psychology.