Regarding a teacher of children who withdrew at a time when no other person was available for hire, so that the child would consequently have to cease his studies: the teacher isn’t permitted to withdraw.

As for what was written concerning the hours during which the children are taught: if the other teachers in that place customarily teach during those hours, he has the right to do so. If this isn’t the local practice, he has no such right.

If the person who hired him was present in the town and knew that the teacher was neglecting his work but remained silent, the teacher can say to him: “You knew that I wasn’t teaching during those hours and accepted it.”

Teshuvot Rabbenu Gershom Me’or ha-Golah, no. 72.