Former pupil able to read front of dam is destroyed (11)
I believe the answer is:
obliterated
'is destroyed' is the definition.
(similar in meaning)
'former pupil able to read front of dam' is the wordplay.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy').
'able to read' becomes 'literate' (I've seen this before).
'front of' says to take the initial letters.
The first letter of 'dam' is 'd'.
'ob'+'literate'+'d'='OBLITERATED'
(Other definitions for obliterated that I've seen before include "trashed" , "made hard to read" , "Utterly destroyed" , "Effaced" , "completely removed" .)