School is on top of multiplication and division (6)
I believe the answer is:
schism
'division' is the definition.
(schism is a kind of division)
'school is on top of multiplication' is the wordplay.
'school' becomes 'sch' (common abbreviation).
'on top of' says to take the initial letters.
The initial letter of 'multiplication' is 'm'.
'sch'+'is'+'m'='SCHISM'
'and' is the link.
(Other definitions for schism that I've seen before include "Breach or division within church" , "Split in church unity" , "Formal division of a church into two" , "Formal split in a church" , "Belief-led division" .)