Dismayed on seeing a pupil with weapons (7)
I believe the answer is:
alarmed
'dismayed' is the definition.
('alarm' can be a synonym of 'dismay')
'on seeing a pupil with weapons' is the wordplay.
'on' says to put letters next to each other.
'seeing a' becomes 'a'.
'pupil' becomes 'l'.
'with weapons' becomes 'armed' (I've seen this before).
'a'+'l' is 'al'.
'al'+'armed'='ALARMED'
(Other definitions for alarmed that I've seen before include "Anxious; disturb" , "Experiencing a sudden sense of danger" , "Flapping" , "Filled with apprehension" , "Terrified" .)