Hits coming from small child in the middle of lesson (6)
I believe the answer is:
smites
'hits' is the definition.
(smiting is a kind of hitting)
'small child in the middle of lesson' is the wordplay.
'small child' becomes 'mite' (I've seen this before**).
'in the' means one lot of letters goes inside another.
'middle of' means to look at the middle letters.
The centre of 'lesson' is 'ss'.
'mite' going inside 'ss' is 'SMITES'.
'coming from' acts as a link.
(Other definitions for smites that I've seen before include "Deals a heavy blow" , "Strikes heavily or kills, biblical word" , "biblical hits" .)