Held centre in class room (4)
I believe the answer is:
cell
'room' is the definition.
(I know that cell is a type of room)
'held centre in class' is the wordplay.
'centre' says to take the centre.
'in' is an insertion indicator.
'class' becomes 'cl' (I've seen this in other clues).
The middle letters of 'held' are 'el'.
'el' put within 'cl' is 'CELL'.
(Other definitions for cell that I've seen before include "Spreadsheet unit" , "Monk's small room" , "Chamber" , "Microscopic unit of living matter" , "celebrated Latin" .)