In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Q: A head teacher ( also called a school principal , or headmaster / headmistress ) is the teacher in charge of a school .
A: 
A head teacher , headmaster , headmistress , head , chancellor , principal or school director ( sometimes another title is used ) is the staff member of a school with the greatest responsibility for the management of the school .