Cut up over start of maths test (4)
I believe the answer is:
exam
'test' is the definition.
('exam' can be a synonym of 'test')
'cut up over start of maths' is the wordplay.
'cut' becomes 'axe' (I've seen this before**).
'up' is a reversal indicator (in down clue: letters go upwards).
'over' says to put letters next to each other.
'start of' indicates taking the first letters.
The initial letter of 'maths' is 'm'.
'axe' written backwards gives 'exa'.
'exa'+'m'='EXAM'
(Other definitions for exam that I've seen before include "Something to sit" , "Scholastic test" , "In brief, a test as in school" , "One might be taken for English" , "Educational test" .)