Burn causing wow in school (6)
I believe the answer is:
scorch
'burn' is the definition.
(scorch is a kind of burn)
'wow in school' is the wordplay.
'wow' becomes 'cor' (both are expressions of surprise).
'in' indicates putting letters inside.
'school' becomes 'sch' (abbreviation).
'cor' inserted inside 'sch' is 'SCORCH'.
'causing' acts as a link.
(Other definitions for scorch that I've seen before include "feel too hot" , "go very fast" , "Singe" , "dry up" , "Damage with heat" .)