Block former pupil over the way with curt disposition (8)
I believe the answer is:
obstruct
'block' is the definition.
('obstruct' can be a synonym of 'block')
'former pupil over the way with curt disposition' is the wordplay.
'former pupil' becomes 'ob' (abbreviation for 'Old Boy').
'over' is a charade indicator (letters next to each other).
'the way' becomes 'st' (**).
'with' means one lot of letters goes inside another.
'disposition' indicates anagramming the letters.
'curt' with letters rearranged gives 'truc'.
'st' placed around 'truc' is 'struct'.
'ob'+'struct'='OBSTRUCT'
(Other definitions for obstruct that I've seen before include "Hamper" , "Get in the way of" , "Block the passage or shut out the view" , "Block, hinder" , "Prevent or hinder movement" .)