Give wrong information to girl heard in class (9)
I believe the answer is:
misinform
'give wrong information to girl' is the definition.
I can't tell whether this defines the answer.
'heard in class' is the wordplay.
'heard' becomes 'mis' (I am not sure about this - if you are sure you should believe this answer much more).
'class' becomes 'form' (form class is a kind of class).
'mis'+'in'+'form'='MISINFORM'
Can you help me to learn more?
(Other definitions for misinform that I've seen before include "Give incorrect gen to" , "Provide with incorrect facts" , "Tell incorrectly" , "Deceive" , "teach badly" .)