Ex-pupil and boy come up with a lout (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
yobbo
'a lout' is the definition.
(I've seen this before)
'ex-pupil and boy come up' is the wordplay.
'ex pupil' becomes 'ob' (abbreviation for 'Old Boy').
'and' means one lot of letters go next to another.
'come up' is a reversal indicator.
'ob'+'boy'='obboy'
'obboy' written backwards gives 'YOBBO'.
'with' is the link.
(Other definitions for yobbo that I've seen before include "Surly youth" , "Rowdy" , "Thug" , "Young troublemaker" , "Hooligan" .)