Senior teacher desires maths to be done differently (12)
I believe the answer is:
headmistress
'senior teacher' is the definition.
(teacher in charge of a school)
'desires maths to be done differently' is the wordplay.
'to be done differently' is an anagram indicator.
'desires'+'maths'='desiresmaths'
'desiresmaths' anagrammed gives 'HEADMISTRESS'.
(Other definitions for headmistress that I've seen before include "School principal" , "Teacher" , "Female school leader" , "Person in charge of a school" .)