Schoolmaster withdrew the assembly from lecture hall (9)
I believe the answer is:
classroom
'hall' is the definition.
(thesaurus)
'schoolmaster withdrew the assembly from lecture' is the wordplay.
I cannot quite understand how this works, but
'from' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'lecture' could be 'class' (academic class) and 'class' is present in the answer.
The remaining letters 'rom' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for classroom that I've seen before include "Teaching environment" , "School space" , "place of education" , "Teaching space" , "Where folk are taught" .)