School is introduction to multiplication and division (6)
I believe the answer is:
schism
'division' is the definition.
(I know that schism is a type of division)
'school is introduction to multiplication' is the wordplay.
'school' becomes 'sch' (common abbreviation).
'introduction to' indicates taking the first letters.
The first letter of 'multiplication' is 'm'.
'sch'+'is'+'m'='SCHISM'
'and' is the link.
(Other definitions for schism that I've seen before include "Splinter group" , "Split in religious body over differences in beliefs" , "Split, often ecclesiastical" , "Split, especially ecclesiastical" , "Split in church unity" .)